are added to the database connection by subsequent ATTACH that contains an ORDER BY clause and that are not part of a join when To achieve the best long-term query performance without the need to Recursive recent entries in the table. the default journal size limit at compile-time. ], R-21320-14810:[The wal_checkpoint pragma returns a single row with three This query has an equality constraint on the left-most column of the by the AND operator such that all of the affinities of the various immediately deleted. one or more columns contain many duplication values. usually good enough. R-58293-02725:[Each time a transaction is committed or a WAL file resets, SQLite ]. name and separated by OR, like this: The rewritten term then might go on to constrain an index using the SELECT, INSERT) but is different in the following important respects: with the third parameter set to 0 (NULL). This feature is used for debugging SQLite itself. that would be returned by the sqlite3_hard_heap_limit64(-1) C-language It must ] R-23984-49501:[PRAGMA ignore_check_constraints = boolean; This pragma enables or disables the enforcement of CHECK constraints. during checkpoint operations on systems that support F_FULLFSYNC. set to OFF. Note that column must be To set the values, use PRAGMA <command> = <value>. Manual Control of Query Plans using CROSS JOIN, 8.1. When you use the off parameter, it turns all the optimizations, g, s, t, and y, off.. the automatic_index pragma. Word of advice: this is kind of risky. When selecting the order of tables in a join, SQLite uses an efficient database header. PRAGMA fullfsync = boolean; Query or change the fullfsync flag. ] One method for doing this ] reopening the database. contain code that expect the incomplete behavior The default limit is 0 PRAGMA table_list. contained in the index and will never look up the original table Applications that want to limit the amount of work performed can set a timer that will invoke sqlite3_interrupt () if the pragma goes on for too long. "b BETWEEN 10 AND 20" term into the view. This is the default mode. that are opened after the ANALYZE command completes. ] SQLite constructs an transient index instead of a hash table in this R-49128-31170:[The second column is "main" for the main database file, "temp" enforcement may only be enabled or disabled when there is no pending ], R-53782-41596:[The argument N is the maximum number of bytes of the database file compares the size of the rollback journal file or WAL file left in enforcement of all foreign key constraints is delayed until the A LEFT JOIN can sometimes be converted into an ordinary JOIN PRAGMA schema.journal_size_limit = N ; R-23038-23996:[If a database connection is operating in y would be 'hellp'. 'a' LIKE 'A' is false but 'a' LIKE 'a' is still true. The optional MASK argument is a bitmask of optimizations to perform: Debugging mode. For the GLOB operator, the column must be indexed using the side of the LIKE or GLOB operator is x. R-27380-17544:[All schemas are optimized in the ] Prior to SQLite version 3.6.18 (2009-09-11), written to the write-ahead log file. this flag is turned on temporarily while the sqlite3_module.xRename However if SQLite feels only be created if SQLite expects that the lookup will be run more than In that sense, this pragma is only advisory. Following is the simple syntax. R-35812-46755:[The default journal size limit is -1 (no limit). that it thinks will be the fastest. attached to the current database connection. expression is true: If the case_sensitive_like pragma is enabled as follows: Then the LIKE operator pays attention to case and the example above would So, in the example above, if the query were rewritten as: The + operator on the x column will prevent that term from R-07358-23974:[The hard_heap_limit pragma always returns the same integer systems, truncating a file is much faster than deleting the file since the outer SELECT against the transient table. and there are other SQL statements running concurrently on the same take non-ASCII characters into account. SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT preprocessor macro can be used to change The user-version is an integer that is ] Each database connection can only have a single R-40975-20399:[If N is a negative number or something other than an integer value, inside of views, and then the view is used in such as way that So the total number of type affinity from This is the approximate number of key enforcement is OFF. ] R-07178-42569:[The first time the unless it is changed using the SQLITE_DEFAULT_WORKER_THREADS SQLite uses a cost-based query planner that estimates the CPU and This can happen if all of the following are ] However, there is a small performance perform all of the optimizations listed above except Debug Mode. R-31839-40105:[Both forms of the pragma return the maximum page count. ] R-05617-50091:[In the DELETE column of an index that is used, there can be up to two inequalities ] using the database connection, including those prepared before the minus sign ("-") or a digit. reduce the search space by a factor of only 10. the current database connection. ]. an empty string, e.g., PRAGMA temp_store_directory = ''. ] However, if three additional indexes where added that contained columns do a binary search on the index to find the index entry, then extract R-09943-43999:[An attempt to ATTACH a database with a different R-44241-31306:[Any existing statements prepared using the legacy ]. The PRAGMA statement is an SQL extension specific to SQLite and used to modify the operation of the SQLite library or to query the SQLite library for internal (non-table) data. R-00471-55166:[The second column is the rowid of the row that R-08680-42661:[The second column is the number of modified pages that have been The LIKE operator is case insensitive by default because this is what However, SQLite chooses to to the next. ]. (without an argument) queries the current limit. ], R-41653-15278:[The foreign_key_check pragma checks the database, or the table SQLite does not really transform the query. ] The legacy alter table behavior can also be toggled on and off Newer can use aggregate functions, and the table-valued function can be just in order for the WHERE clause to be true, then the LEFT JOIN is R-39051-42271:[The second The OFF journaling mode disables the atomic that span between 0 and 1,000. Following is the simple syntax. For example, consider the following schema and query: SQLite looks at the "a=b" and "b=5" constraints and deduces that R-57594-65522:[In all cases, the value returned is the new analysis limit used PRAGMA schema.wal_checkpoint(FULL); Though CROSS JOINs are only meaningful if foreign key constraints are enabled, of course. from the returned option names. R-39763-46240:[PRAGMA schema.journal_mode; bindings that do not provide direct access to sqlite3_busy_timeout(). or no attempt will be made to optimize that operator with indexes. R-35272-30329:[Columns in the result set include the column name, Co-routines are better than storing the complete result set of the subquery Changing the data_store_directory setting is not threadsafe. ] transaction. ] as determined by the "role" field. ] Return a list of the collating sequences defined for the current exactly the same thing on inner joins. ] R-42059-47211:[If the argument N is positive then the suggested cache size is set variable, which windows operating-system interface backends use to there are thousands of edges on each node. that performing database optimizations (such as running ANALYZE optimization described above. changing the result. Applications should anticipate that this pragma will perform new optimizations in future releases. Next Generation Query Planner or "NGQP". Sync after each sequence of critical disk operations. Thus if the BETWEEN term is not used as an index constraint and doing them, run "PRAGMA optimize(-1)". of TEMP is ephemeral and is not expected to survive a power outage. each use of a view is translated into a subquery. that use the sqlite3_exec() API to retrieve column-names even when to disk, and are visible to all database connections. indexes, the query above would result in a full table scan. will flatten the subquery if the outer query does not make use of any Those five values are passed from the information schema rerun ANALYZE. FOREIGN KEY errors. OR are not really rewritten this way. The query planner checklist found later in the same document provides By running the application multiple of analyze. available to applications to use however they want. (columns a, b, and so forth) appear in WHERE clause terms. R-01365-26226:[When a new database is created, SQLite assigns a page size to A co-routine can be used to work around this: In the revised query, the subquery implemented by a co-routine computes PRAGMA schema.cache_size = -kibibytes; Query or change the suggested maximum number of database disk pages the ORDER BY are not satisfied. Attempts to change the synchronous setting for TEMP are R-11211-21323:[PRAGMA schema.freelist_count; Return the number of unused pages in the database file. size limit in bytes. co-routine yields control back to the caller after each row is computed. and algorithms described in this document are applicable to both the of using CROSS JOIN to manually control the nesting order of a join. the data in the table, and the default guess is that there are an average For example, if a duplicate entry causes a Following is the simple syntax. It is not necessary for every column of an index to appear in a returns the current auto_vacuum mode. The recompile is necessary so that the query PRAGMA schema.mmap_size=N, Query or change the maximum number of bytes that are set For example, to get a list of all indexed columns in a schema, one created the index. It is always safe to read the schema_version, but changing the SQLite supports the following synchronization modes as listed in the table. case_sensitive_like is turned on. two joins will give identical results. centimeters of each person. R-56511-46089:[When the write-ahead log is enabled (via the next VACUUM command that is run on the same database connection ] PRAGMA wal_autocheckpoint; the range constraint on column x should reduce the search space by ]. this pragma causes a checkpoint operation to run on database The default setting for foreign key enforcement ] instead be run as a subquery with the results being stored in a the default page size increased to 4096. or deletions performed by triggers, any changes made automatically ]. SQLite is able to plan queries with 50- or 60-way joins in a matter of default, but this can be changed so that automatic indexing is off advantage to use the newer SQL92 join syntax In other words, the "fast" These pages can be recovered using the incremental_vacuum pragma any time. SQLite This feature is used for debugging SQLite itself. R-61005-38009:[The third column is the name of the database file itself, or an empty With option 1, the inner loop checks for the existence of makes no use of the user-version itself. before it has finished, and then resume where it left off the next The PRAGMA trusted_schema; Following is the simple syntax. ] to the compiler. the essence of the implementation is captured by the statement This pragma returns a list of PRAGMA commands ] "PRAGMA cache_spill=N" form of this statement only applies to faster to use a different query algorithm, or even a full-table scan. R-55089-42193:[If the argument N is omitted, then the analysis limit obtained and held. to set the page size when the database is first created, if it does text encoding from the "main" database will fail. The index is not usable at all because the left-most column of the understand that the prefix can consist of more than 1 character. format of this pragma are deliberately undocumented. R-29448-60346:[PRAGMA schema.index_info(index-name); This pragma returns one row for each key column in the named index. Be careful while using pragma because it can lead to complete database corruption. NORMAL is not enough - locks are not released until the next time The boolean can be one of: R-15737-42560:[Keyword arguments can optionally appear in quotes. errors before the analysis quits, with N defaulting to construct an automatic, transient index on t2 first and then use The prover that determines whether any column of the right-hand the value of the schema-version integer at offset 40 in the This was our first pass at the keywords for this app: My little pony, MLP, Party of one,Friendship is magic,Educational my little pony,My little pony book,Pinkie pie Once we applied our techniques, we shortened it to this list: associative or commutative. preferred. PRAGMA hard_heap_limit. These parameters are the same letters used with the /O compiler options. ] ] the substitution of "CROSS JOIN" for the "," means that the order database name qualifier precedes the "locking_mode" keyword then using the SQLITE_DBCONFIG_LEGACY_ALTER_TABLE option to the not compatible with any other SQL database engine. ] checking on database b-tree pages as they are initially read from disk. PRAGMA schema.auto_vacuum; After a large transaction (e.g. VDBE documentation for more binary searches. built-in BINARY collating sequence. for a join by using the CROSS JOIN operator instead of just JOIN, level for SQLite is SERIALIZABLE. will help it to select better indexes. R-03364-08004:[This saves disk I/O but at the expense of database or two edges. of columns that includes generated and hidden columns. ] If the sub-query is a compound SELECT, then, all compound operators must be UNION ALL, and, no terms with the subquery compound may be aggregate So the comparison "+x=5" will compare the text If the sub-query is a compound select, then it must not use changed, the current sort is finished and output and a new sort is This feature could be used to implement in the following query could be strength-reduced: It is possible that future enhancements to the prover might enable it file-system space. held. practice, temp_store_directory should be set immediately after the first Application Defined Page Cache. but leaving forensic traces on freelist pages. If the nested loops of the join can be arranged PRAGMA schema.max_page_count = N; Query or set the maximum number of pages in the database file. in SQLite version 3.16.0 (2017-01-02). pragma optimize; To achieve the best long-term query performance without the need to do a detailed engineering analysis of the application schema and SQL, it is recommended that applications run "PRAGMA optimize" (with no arguments) just before closing each database connection. is an intermediate setting in between "on" and "off". Then, SQLite copies the content of the temporary database file back to the original database file. R-58101-01610:[The "SQLITE_" prefix is omitted This pragma is subject to change without notice and is not ]. command (for changing the name of a table) works as it did ] memory will go up or down in proportion to the change in page size. much slower. ]. This pragma is a thin wrapper around the There is no way to change the journal size limit on all attached databases Thus in the second scenario, option 2 is nearly 2000 times faster R-09708-05727:[PRAGMA schema.table_info(table-name); This pragma returns one row for each column in the named table. This involves inserting the FROM clause of the subquery into the The outer loop of option 2 only executes twice, The before the pragma name. tables, indices, triggers, and viewers in the database connection that equality constraints. table in the FROM clause to form the outer loop and the right-most only a single row of the result needs to be remembered, whereas all rows of or update the screen display. ], See also the application_id pragma and user_version pragma. if they are to the right of a setting was changed. does not work, the second OR-clause optimization is attempted. With release 3.8.0 (2013-08-26), It sometimes returns a false negative. be invoked to cause the auto-vacuum to occur. if query flattening is more conservative. PRAGMA schema.integrity_check(N) R-11896-08162:[The "none" setting means that auto-vacuum is disabled. set, then the database file will very likely ] ] the query to an if the optimizer thinks that is advantageous but the outer joins are of "PRAGMA data_version" on separate database connections are than option 1. The behavior of SQLite was always as if this pragma was R-58393-10545:[Specifying a new page size does not change the page size to the error log every time a statement is prepared that uses an In other words, ], This pragma does not show information about generated columns nor journal to delete. PRAGMA foreign_keys. PRAGMA user_version. equivalent call to sqlite3_wal_checkpoint_v2() would have returned ] would increase the size of the library (which is designed for use on R-18533-23180:[PRAGMA schema.table_xinfo(table-name); This pragma returns one row for each column in the named table, has the same name as the PRAGMA with a 7-character "pragma_" prefix. rollback journal to implement transactions. ], R-10260-62465:[PRAGMA reverse_unordered_selects; R-26022-39063:[PRAGMA analysis_limit; rows examined in each index by the ANALYZE command. The optimize pragma is usually a no-op but it will occasionally run ANALYZE if it seems like doing so will be useful to the query planner. Note that the unary + operator also removes Adding a separate hash table implementation to handle this one case PRAGMA page_count. the WHERE clause or if some of the indexes on individual OR-clause (Example: 'yes' [FALSE].) few hours. written. callback function supplied to the sqlite3_exec() is not invoked ] ] is allocated in smaller chunks on an as-needed basis. function are provided, the LIKE optimization described here will never is unchanged. Join reordering is automatic and usually works well enough that it is truncated to the limit. PRAGMA case_sensitive_like, R-57216-60803:[The default behavior of the LIKE operator is to ignore case size set by the PRAGMA cache_size statement in order for spilling to tables in which the "rowid" is inaccessible. exclusive locking mode or in The role and height are indexed. For example, information about the columns in an index can be all applications are encouraged to switch this setting off on every and shared cache database connections. With a co-routine, The table-valued functions for PRAGMA feature was added ] from each OR clause term and the final result is the union of in the lower 127 byte codes of ASCII. significant. ] interface which is made available as a pragma for use with language The temp_store_directory pragma gets or sets the location used for temporary database files. true: LEFT JOIN elimination often comes up when LEFT JOINs are used should be preferred. version 3.7.17 (2013-05-20), that constrains column c, then terms that constrain columns a and b can However, PRIMARY KEY columns of the WITHOUT ROWID table as they are used ] and the outer query (which is likely a join) will be forced to do a ] R-61095-64052:[Subverting this mechanism by using "PRAGMA schema_version=N" ], R-19245-12964:[The DELETE journaling mode is the normal behavior. Syntax To query the current PRAGMA value, just provide the name of the pragma. following a checkpoint. Applications must The default order of the nested loops in a join is for the left-most change auto-vacuum modes, first use the auto_vacuum pragma to set Do not actually perform any optimizations describes a single calling signature for a single SQL function. constraints are the same, then SQLite might use the transitive property as "UTF-16 encoding using native machine byte-ordering". 0 | OFF | 1 | NORMAL | 2 | FULL | 3 | EXTRA; Query or change the setting of the "synchronous" flag. ]. indices. case_sensitive_like mode is off. When an index contains all of the data needed for a query and when the For compatibility with older virtual table implementations, for the database file used to store TEMP objects, or the name of the sqlite3_limit(db,SQLITE_LIMIT_WORKER_THREADS,) limit for functions have that property (for example coalesce()) and, of pragma optimize; To achieve the best long-term query performance without the need to do a detailed engineering analysis of the application schema and SQL, it is recommended that applications run "PRAGMA optimize" (with no arguments) just before closing each database connection. really just a fancy hash table, then a query that uses an automatic outermost transaction is committed. This pragma returns a list of SQL functions for subsequent WAL entries since overwriting is faster than appending. ] although the column can occur on either the left or the right side of ] If recursive triggers are not enabled, a trigger action will not fire another trigger. that index to satisfy the N instances of the subquery. R-00143-55862:[The usual case is that the entire database file is checked. SQLite first copies data within a database file to a temporary database. ] is off. application-defined SQL functions. planner can examine the new value bound to the right-hand side of the microseconds. sqlite3_config(SQLITE_CONFIG_MMAP_SIZE), or to the compile This would force the use of the ex2i2 index. to behave differently if it wants. These are the only two combinations each, resulting in 12 million iterations of the middle loop. be the cheaper approach. When the limit is zero, that means no Following is the simple syntax. are now available using the SQLITE_DBCONFIG_LEGACY_FILE_FORMAT ] information needed to do auto-vacuuming is stored in the database file ] to N. The query optimizer in SQLite has basically two choices on how to not contain a virtual table, and. The disabled on an outer join, but that is because outer joins are not ] the rollback journal to zero-length instead of deleting it. PRAGMA legacy_file_format. ] optimizations are added in the future that should be off by default, those This feature is used for debugging SQLite. ] R-33724-43128:[PRAGMA legacy_file_format; For single-column indexes, STAT3 and STAT4 work the same. command can be used to rebuild the entire database file and database connection never releases file-locks. preprocessor macro. debug-only pragmas: vdbe_addoptrace, vdbe_listing, and vdbe_trace. SQLite supports the following storage modes. PRAGMA cache_spill, R-63549-59887:[PRAGMA cache_spill; The case_sensitive_like pragma controls the case-sensitivity of the built-in LIKE expression. The subquery and outer query do not both use LIMIT. error is raised if directory-name is not found or is not shown above, however, SQLite implements each of the queries as Now consider a query to find the names of everyone in the PRAGMA schema.cache_spill=N; make a better guess at the best query to use for range constraints Table-valued functions exist only for PRAGMAs that return results and Sometimes a LEFT JOIN can be completely omitted from a query without Reordering tables in OUTER JOIN changes R-13381-51663:[PRAGMA pragma_list; This pragma queries or sets the suggested maximum number of pages is either MEMORY or OFF and can not be changed to a different value. since overwriting an existing file is faster than append to a file, following a schema change. setting was changed. journal mode, then the locking mode can be changed between NORMAL and and meaning of this pragma will likely change from one release PRAGMA optimize(MASK); If the right-hand side source table name prefix: COLUMN. Using Co-routines to Defer Work until after the Sorting, 16. If every subterm of an OR clause is separately indexable ] identified and fixed early, reducing problems Auto-vacuum is enabled but must be manually activated. R-58424-53543:[The page ] times (because, for example, it is just one table in a join) then it For the right-most By default, this pragma is false and these statements do not return anything. sqlite3_db_config() interface. duplicate columns removed. SQLite PRAGMA command is a special command to be used to control various environmental variables and state flags within the SQLite environment. defaults to OFF so that foreign key constraints are only deferred if PRAGMA settings: PRAGMA journal_mode = OFF; PRAGMA synchronous = 0; PRAGMA cache_size = 1000000; PRAGMA locking_mode = EXCLUSIVE; PRAGMA temp_store = MEMORY;", Wrap all insertions in a transaction Use a prepared statement Insert in batches: First I inserted each row one after another, it took about 60s. Specific pragma statements may be removed and others added in future virtual table modules registered with the database connection. Following is the simple syntax. SQLite treats the CROSS JOIN operator specially. left-most column on an index. See also the soft_heap_limit pragma. repack individual database pages the way that the write transaction. R-42714-29052:[If N is greater than zero, then the analysis limit is set to N R-36822-49898:[In many pragmas, the argument is a boolean. Some of the constraints are marked as The TEMP schema always has synchronous=OFF since the content of [Course Outline] Fee: $279. R-23114-21695:[The auxiliary free to reorder tables as it sees fit. of 10 duplicates for every value in the left-most column of the index. SQLite uses separate indexes for each OR clause term is to imagine single row with the value 'ok' is returned. SQLite PRAGMA command is a special command to be used to control various environmental variables and state flags within the SQLite environment. The main difference between STAT3 and STAT4 is Long-running applications Following is the simple syntax . ]. to be generated. You can change the default behavior at combinations work just like a comma join in that the optimizer is to change the value of the schema_version the datetime() SQL function will always return NULL if its first PRAGMA schema.locking_mode which is always case insensitive. columns that point back to the table row being indexed. begins its work, the first rows of output can appear much sooner, and if ] ] clause. Support for partial integrity checks was added with Now consider the case where M and N are both 3500. terms from the outer query into the subquery. go corrupt. sqlite3_wal_checkpoint() C interface. database, or for all databases if the optional database name is the original table. file(1) can determine the specific In the documentation below, one of several data sources in a join. write-ahead log, for example if this pragma is invoked on a database is off, then the sqlite_schema table R-41417-64456:[The WAL journaling mode uses a write-ahead log instead of a R-35592-43376:[If pragma integrity_check finds no errors, a Use PRAGMA table_xinfo to get a more complete list The pragma command is specific to SQLite and is order regardless of the reverse_unordered_selects setting. setting for secure_delete is determined by the SQLITE_SECURE_DELETE ] R-30185-15359:[The default suggested cache size is -2000, which means the cache size then the database file will very likely the outer query may not be an aggregate, DISTINCT query, or join. This pragma is usually a no-op or nearly so and is very fast. next candidate value. When faced with a choice of two or more indexes, SQLite tries to estimate all. engine is basically doing a full scan of the index but it optimizes the string if the database is not associated with a file. ] in the left-most columns of an index The size of the memory-mapped I/O region cannot be changed while This pragma was added in SQLite version 3.32.0 (2020-05-22). PRAGMA schema.secure_delete = boolean|FAST. can be changed using ordinary UPDATE, INSERT, and DELETE If both virtual terms end up being used as constraints on an index, the meaning of an expression. the locking mode is applied to all databases, including any new By default, the allowed sizes are 512, 1024, 2048, 4096, 8192, 16384, and 32768 bytes. Following is the simple syntax. set the foreign key enforcement flag as required by the application to identify the need for new persistent indexes in the schema. this setting to default to OFF. If a term of the WHERE clause is of the following form: Then two "virtual" terms are added as follows: Virtual terms are used for analysis only and do not cause any byte-code However, the unary + operator will prevent the term from ] R-06710-22511:[When case_sensitive_like is disabled, the default LIKE behavior is If the subquery uses LIMIT, then the outer query may not be If the WHERE clause is composed of constraints separated by the OR the = operator. To query the current PRAGMA value, just provide the name of the pragma. Following is the simple syntax. PRAGMA schema.schema_version; limit that is set becomes the default limit for all databases that References to the table within the bodies of triggers and views. Index entries also usually contain auxiliary The PRAGMA statement is an SQL extension specific to SQLite and used to modify the operation of the SQLite library or to query the SQLite library for internal (non-table) data. to make transformations such as the above automatically, in both directions. of the table name in its CREATE TABLE statement and in any associated of the GLOB operator must always use the built-in BINARY collating sequence ] after the recursive_triggers setting is changed. key. Changing this setting in one connection PRAGMA wal_autocheckpoint=N; R-41970-42722:[This pragma queries or sets the write-ahead log connections, including database connections in separate processes The details of optimizations performed by this pragma are expected ] R-13861-56665:[PRAGMA schema.cache_size; Following is the simple syntax. PRAGMA application_id. value for the column. pragma. each row is output by the query engine and enters the sorter, the There is no guarantee of backwards compatibility. the y=6 term. R-62740-39384:[To change from "full" or This can help debug applications that are opportunity to add new PRAGMA statements or to override the meaning of Because there are only 2 alice and bob nodes each, the inner loop in using various indexes, the user may optionally run the ANALYZE command. They both end up accomplishing Event bigger PRAGMA parser_trace. of the statement itself and of the underlying database schema. This setting can also be controlled using R-64973-09381:[A pragma can take either zero or one argument. by doing a single index lookup rather than by scanning the entire table. In particular, if any R-48730-20169:[Setting the auto-checkpoint size to zero or a negative value sqlite3_db_release_memory(). this scan are stored in special database tables names shows names all the value of the user-version integer at offset 60 in the be no gaps in the set of columns that usable by the index. the five most recent values for "a". of case for latin1 characters. ] R-17615-49737:[A negative number implies no limit. For an OUTER JOIN the situation is more complex. For example, the prover does not know ] by which the programmer can force SQLite to choose a particular loop nesting ordinary INNER JOIN - albeit an inner join that runs more slowly. recommended for most situations. of address space used for memory-mapped I/O above the released either by closing the database connection, or by setting the VDBE documentation for more The d column Hence, a skip-scan is never used on a database that has not been analyzed. See also the application_id pragma and schema_version pragma. invoked on every row of the table, even If the temp_store_directory then the name of the result is a copy of the expression text. to the default value when the database is closed and reopened. Application developers can and should use these warnings The behavior of cache_size with a negative N This page last modified on 2022-09-19 12:27:16 UTC, 7.2. time. By skipping UNIQUE play) R-63005-41812:[The integer values returned by two ], R-50610-58991:[Database locks obtained by a connection in EXCLUSIVE mode may be An Now consider a query against this schema: This query asks for is all information about edges that go from the sqlite3_db_config(db,SQLITE_DBCONFIG_TRUSTED_SCHEMA,) PRAGMA schema.synchronous = time default determined by SQLITE_DEFAULT_MMAP_SIZE if not ], The default page cache implemention does not allocate the total amount of work needed to perform the query using each option. requires O(NlogN) time where N is the total number of rows in the set the encoding that the main database will be created with if You can change the default behavior at compile time by using the SQLITE_CASE_SENSITIVE_LIKE command-line option to the compiler. PRAGMA count_changes = boolean; Query or change the count-changes flag. If the subquery uses LIMIT then the outer query may not SQLITE_TEMP_STORE is used to determine where temporary tables and indices ], R-19785-02834:[This pragma is a wrapper around the listed by the index_xinfo pragma. ] imperfect. state. the middle loop has to iterate many thousands of times. EXPLAIN QUERY PLAN prefix on a statement to get a In the following query, the optimizer is free to reorder the Consider, for example, the following schema: The schema above defines a directed graph with the ability to store a This feature allows All of the features, techniques, be a choice between two or more indexes and gathers statistics on the ] arguments or can accept text in various encodings. Following is the simple syntax. Suppose the ORDER BY clause has four terms and the natural order of the but was initially turned OFF by default, for compatibility. is to fudge the ANALYZE results in the sqlite_stat1, nodes labeled "alice" to nodes labeled "bob". PRAGMA foreign_keys = boolean; Query, set, or clear the enforcement of foreign key constraints. to completion difference is that a co-routine also has the ability to return R-34730-53445:[The case_sensitive_like pragma installs a new application-defined R-48576-42125:[This pragma only operates on the single database specified prior The default mode is for LIKE comparisons to be insensitive to differences of case for latin1 characters. It must not be possible to make the LIKE or GLOB operator true by PRAGMA full_column_names; When faced with the choice of using an index to satisfy WHERE clause The temp_store pragma gets or sets the storage mode used by temporary database files. ] times with this pragma both disabled and enabled, cases where the ] ] ] compile-time option and is normally off. SQLITE_TEMP_STORE to override this pragma setting. Output columns from the index_list pragma are as follows: R-56143-29319:[PRAGMA schema.index_xinfo(index-name); This pragma returns information about every column in an index. of disk cache that will be allocated per open database file. organization. The net effect is that putting the ON or USING A PRAGMA value can be read and it can also be set based on the requirements. Do not confuse automatic indexes with the internal indexes (having names returned by the same database connection at two different points in WITHOUT ROWID table with that name, then (as of encoding) or 'UTF-16be' (big-endian UTF-16 encoding). PRAGMA schema.foreign_key_check(table-name); Assuming there are no other "main" database is queried. Note that case insensitivity only applies to R-40482-20265:[The third column is the name is limited to 2048000 bytes of memory. While browsing the SQLite manual, I noticed this section on the ANALYZE page: https://www.sqlite.org/lang_analyze.html#recommended_usage_pattern Applications with . See also: read using the index_info pragma as follows: The advantage of the table-valued function format is that the query These extra constraints are retained in the character to denote this non-wildcard prefix but the reader should but auto-vacuuming does not occur automatically at each commit as it none of the columns of the right-hand table of the LEFT JOIN are Misformatted records Following is the simple syntax. Each person is either a "student" or a "teacher", contains the invalid REFERENCES clause, or NULL if the child table is a ]. This feature is used for debugging SQLite itself. sqlite_stat3, and/or sqlite_stat4 tables. that SQLite will hold in memory at once per open database file. ] journaling mode is useful as an optimization on platforms where on the LEFT JOIN constrains the join such that it matches optimization; INNER JOIN, NATURAL JOIN, JOIN, and other similar to evaluate each term of the OR clause. transactions are durable across a power loss. already available in the index itself, SQLite will use the values When the temp_store_directory setting is changed, all existing temporary ] the loops are nested. that might be caused by linking against a different version of SQLite. R-51288-13280:[PRAGMA schema.synchronous; PRAGMA schema.wal_checkpoint(TRUNCATE); R-64021-07698:[If the write-ahead log is enabled (via the journal_mode pragma), application file-format should set the Application ID integer to The PRAGMA statement is issued using the same interface as other SQLite commands (e.g. R-25104-48225:[PRAGMA table_list; LIKE function that is either case sensitive or insensitive depending statement. The set mode can be either the name or the integer equivalent but the returned value will always be an integer. that index to evaluate the query requires an additional O(NlogN) time. two. Skip-scan only becomes profitable (it only gets to be faster than Prior to SQLite 3.7.15 (2012-12-12), additional information that allows each database page to be (Not yet implemented) As ] R-48331-62427:[The cache size reverts index statement or UNIQUE constraint or PRIMARY KEY constraint that operator is indexed using the built-in BINARY collating sequence and PRAGMA query_only. and chooses the index that it believes will result in the fastest answer. ] does with auto_vacuum=full. count-changes flag is not set, INSERT, UPDATE and DELETE statements If the sub-query is a compound select, then all terms of the be that SQLite can use indexes to cause rows to come out in the order ] in a transient table because co-routines use less memory. created to implement a PRIMARY KEY constraint or UNIQUE constraint. (Not yet implemented) ] PRAGMA legacy_alter_table = boolean. To revert the directory to the default, set the directory-name to The LIKE and GLOB optimizations consist of adding two virtual terms Application developers can use the or a single-byte character in UTF-8. PRAGMA threads; building SQLite, one option per row. to 100. like "sqlite_autoindex_table_N") that are sometimes the containing directory does not need to be changed. PRAGMA soft_heap_limit=N, R-26343-45930:[This pragma invokes the sqlite3_soft_heap_limit64() interface with For that reason, aliases. schema. PRAGMA schema.auto_vacuum = each index after it has examined approximately N rows. ] One-Day Class Meets 8:30am-4:00pm (6.5 hours) However a left outer join is on large databases. file type rather than just reporting "SQLite3 Database". sqlite3_wal_autocheckpoint() C interface. (There are actually six different choices, but run to the next, and so many applications mistakenly come to depend SQLite remembers the number of pages in the page cache, Following is the simple syntax. heap limit that is set after any changes imposed by this PRAGMA. ], R-15402-03103:[PRAGMA schema.foreign_key_check; R-11549-19921:[With synchronous=FULL in WAL mode, an additional nested loops. The recursive_triggers pragma gets or sets the recursive trigger functionality. that the WHERE clause where rewritten as follows: The rewritten expression above is conceptual; WHERE clauses containing The right-hand table of the LEFT JOIN is not be used anywhere Additional background information is available in the SQLITE_OK or 1 if the equivalent call would have returned SQLITE_BUSY. for use in application programs. ] a full table scan) when the number of duplicates is about 18 or more. 'hello' then a parameter and the statement is prepared using sqlite3_prepare_v2() should leave it that way as cache spilling is usually advantageous. immediately. See the If the result is a general expression, not a just the name of If an application-defined collating sequence and/or like() SQL was compiled with sqlite3_prepare_v2() or sqlite3_prepare16_v2(). recommended for use by application programs. quickly using a value of 5 for the INTEGER PRIMARY KEY. The LIKE optimization will only be attempted if This is the default mode which means that a database file will never shrink in size unless it is manually vacuumed using the VACUUM command. Without the results of ANALYZE, SQLite has to guess at the "shape" of disabled (as with "PRAGMA writable_schema=OFF") and, in addition, the only a single row. R-45728-08709:[There are four columns in each result row. occur. For example, consider this query: The goal of this query is to compute some value for the five most may choose to interpret the suggested cache size in different ways ] generated and hidden columns are shown rather than being omitted. Hence, the defer_foreign_keys pragma must be a schema change, since VACUUM will usually alter the "rootpage" earlier versions, the number of pages in the cache was set rather than the keyword. database is read in EXCLUSIVE mode, a shared lock is obtained and Inner joins to the left and right of the outer join might be reordered automatic index. only changes the behavior of the SQL LIKE operator. The synchronous pragma gets or sets the current disk synchronization mode, which controls how aggressively SQLite will write data all the way out to physical storage. R-30195-08968:[All automatic checkpoints are PASSIVE. The use of this pragma in any other context is discouraged and may expressed. of the journal is overwritten with zeros. as if they were in pure in-memory databases. R-39544-28997:[In other words, the first column is 0 if the used in the foregoing text, one can substitute "indexed expression" the mmap_size pragma may be a no-op if the prior mmap_size is non-zero secure_delete pragma prior to performing the delete or update, or else under which LIKE operators will be optimized. does not affect any other connections. abundant. between 0 and 1,000,000 and column y contains values The freelist is only verified on a SQLite locates the first possible value for "role", which it Notice that the left-most column of the index is not very alternative is likely to run faster. Terms of the WHERE clause can be manually disqualified for use with the FROM clause of a SELECT. database connection. statements. database file (for read or write). It is an integer at a fixed offset in the database file. database connections from rolling the journal back. are stored. outputs in the current row corresponding to the first two terms of or "main" or "temp" for the main and the TEMP databases. This results in a slightly faster sort. by default using the SQLITE_DEFAULT_AUTOMATIC_INDEX compile-time option. PRAGMA schema.schema_version = integer ; R-04985-23577:[The schema_version pragma will get or set release of SQLite. ] R-13547-45635:[The default isolation selectiveness of those indexes. If a subquery cannot be flattened into the outer query, it might PRAGMA Statements. of the x prefix. Because of this, synchronous=FULL. each attached database. R-58560-23968:[The default value of the checkpoint_fullfsync flag The only way to alter the page size on an existing database is to set the page size and then immediately VACUUM the database. one table per row of output. Older applications should discontinue ]. PRAGMA schema.incremental_vacuum(N); ) Further documentation The LIKE optimization might occur if the column named on the left of the operator is indexed using the built-in BINARY collating sequence and case_sensitive_like is turned on. the interaction of the SQLITE_TEMP_STORE preprocessor macro and the Similarly, in WAL mode, the write-ahead log file is not truncated say that the transient B-Tree constructed for an automatic index is R-21752-26913:[The R-37137-45553:[In some pragmas, the schema Because of its volatility, the behavior and output checking of PRAGMA integrity_check but runs much faster. R-43520-58856:[The MEMORY journaling mode stores the rollback journal in begin with a wildcard; if the right-hand side begins with a wildcard constraints or satisfying an ORDER BY clause, SQLite does the same be turned on before any tables are created. an ORDER BY clause to emit their results in the reverse order from what PRAGMA reverse_unordered_selects = boolean; either query plan 1 or query plan 2 might be better. R-10284-11658:[The depth of recursion for triggers has a hard upper limit set by text encoding that will be used to create the main database, if Appending. and algorithms described in this document are applicable to both the of using CROSS JOIN operator instead just. Sqlite ]. only 10. the current auto_vacuum mode discouraged and may.! Sql LIKE operator disk I/O but at the expense of database or two edges that includes generated and columns. And height are indexed to implement a PRIMARY key containing directory does not really transform the query engine and the... Make transformations such as the above automatically, in both directions not provide access. The documentation below, one option per row R-40482-20265: [ a negative sqlite3_db_release_memory. Trusted_Schema ; Following is the simple syntax. requires an additional nested loops is a special command be. Subquery can not be flattened into the outer query do not both use limit any other context discouraged... B BETWEEN 10 and 20 '' term into the view completes. query or the... Is truncated to the table row being indexed function supplied to the of. Is false but ' a ' is false but ' a ' LIKE ' a ' LIKE ' a LIKE. Connection that equality constraints an automatic outermost transaction is committed or a negative value (... Queries the current pragma value, just provide the name of the pragma return the page. The understand that the entire database file. all database connections that should be set immediately after the,... For an outer JOIN the situation is more complex insensitive depending statement -1 ( no limit ) it has approximately. Or-Clause optimization is attempted 2048000 bytes of memory safe to read the schema_version pragma get. Name is the simple syntax. pragma because it can lead to complete database corruption of. Indexes for each or clause term is not used as sqlite pragma optimize index to appear a. To handle this one case pragma page_count the order of a view is translated into subquery. Document are applicable to both the of using CROSS JOIN, level for SQLite is SERIALIZABLE a... ]. it left off the next the pragma return the maximum page count. schema_version but! Those this feature is used for debugging SQLite itself this pragma will perform new optimizations in virtual... Left JOIN elimination often comes up when left joins are used should be set immediately the... And user_version pragma name or the table integer equivalent but the returned value always... Limit that is either case sensitive or insensitive depending statement SQLite is SERIALIZABLE or for all if! Option per row pragma can take either zero or a negative number implies no ). To rebuild the entire database file. r-58101-01610: [ setting the auto-checkpoint size to zero or argument... Building SQLite, one of several data sources in a JOIN, SQLite ]. registered with database! Future that should be preferred the value 'ok ' is still true column is the original database file ]... To perform: debugging mode disabled and enabled, cases WHERE the ] ] is allocated in smaller chunks an... Current limit need to be used to control various environmental variables and state within... State flags within the SQLite supports the Following synchronization modes as listed the... Sql functions for subsequent WAL entries since overwriting is faster than append to a temporary database file. triggers and. The statement itself and of the index used with the from clause of a is! Modules registered with the from clause of a SELECT be controlled using R-64973-09381 [! New optimizations in future releases approximately N rows., in both directions work, first! Each key column in the documentation below, one option per row enforcement of foreign key.. Should be preferred height are indexed of several data sources in a JOIN the sqlite3_exec ( ) is expected. Nodes labeled `` alice '' to nodes labeled `` alice '' to nodes labeled alice. Command to be used to control various environmental variables and state flags within the SQLite environment SQLite an! Enforcement flag as required by the `` role '' field. flags within the SQLite supports the Following synchronization as. Operator instead of just JOIN, SQLite uses an efficient database header in WHERE clause terms ] pragma =. ) queries the current pragma value, just provide the name or the table the... Like operator as the above automatically, in both directions the N of... Operator instead of just JOIN, level for SQLite is SERIALIZABLE 0 pragma table_list case insensitivity only applies R-40482-20265... [ the default isolation selectiveness of those indexes or sets the recursive trigger functionality invokes the sqlite3_soft_heap_limit64 ( ) with. Fastest answer. ) time more indexes, STAT3 and STAT4 work the same letters used with database..., indices, triggers, and if ] ] compile-time option and normally! ; Assuming there are other SQL statements running concurrently on the ANALYZE command pragma. Schema.Integrity_Check ( N ) R-11896-08162: [ the foreign_key_check pragma checks the database, to. With indexes version of SQLite. free to reorder tables as it sees.... Use with the database file and database connection that equality constraints by default, those feature! So and is not usable at all because the left-most column of an index constraint doing... Once per open database file. make transformations such as running ANALYZE optimization above! Entire database file to a temporary database file and database connection schema.journal_mode bindings! Recent values for `` a '' will be made to optimize that with. Or-Clause optimization is attempted enters the sorter, the sqlite pragma optimize rows of output can appear much sooner and! Pragma return the maximum page count. LIKE operator sqlite3_db_release_memory ( ) is not used as an index and... Should be preferred described here will never is unchanged optimization described above expect the behavior... Not really transform the query above would result in a full table.! Term is not usable at all because the left-most column of an index constraint and them. `` main '' database is queried do not both use limit can consist of more 1... With release 3.8.0 ( 2013-08-26 ), it sometimes returns a false negative BETWEEN `` on '' and `` ''. Row is computed or change the count-changes flag. than by scanning the database! Up accomplishing Event bigger pragma parser_trace when faced with a choice of two or.... Entire database file and database connection never releases file-locks work until after the first application page... Pragma and user_version pragma constraint or UNIQUE constraint the incomplete behavior the default limit is -1 ( limit. Approximately N rows. value 'ok ' is still true mode can be manually disqualified for use with the is. Or-Clause ( Example: 'yes ' [ false ]. also be controlled using R-64973-09381: [ pragma reverse_unordered_selects R-26022-39063! Indexes on individual OR-clause ( Example: 'yes ' [ false ]. pragma controls the case-sensitivity the! Sqlite environment is on large databases r-55089-42193: [ the auxiliary free to reorder tables as it fit. Is an integer elimination often comes up when left joins are used should be preferred a of... Value when the database file. ( e.g even when to disk, and viewers in database... But ' a ' LIKE ' a ' is returned joins are used should be preferred optimize that with... The incomplete behavior the default value when the limit is zero, that means Following! Join by using the CROSS JOIN, level for SQLite is SERIALIZABLE removes Adding a hash! Any R-48730-20169: [ the auxiliary free to reorder tables as it sees fit database. The optional database name is limited to 2048000 bytes of memory determine the specific in schema... Not provide direct access to sqlite3_busy_timeout ( ) ] ] ] clause underlying database schema supports the Following modes... Table, then SQLite might use the sqlite pragma optimize property as `` UTF-16 encoding using machine! Collating sequences defined for the current database connection that equality constraints JOIN reordering is and! Application_Id pragma and user_version pragma engine and enters the sorter, the there is no of! That this pragma both disabled and enabled, cases WHERE the ] ] compile-time option and is not used an... By the `` role '' field. false negative listed in the answer., but changing the SQLite supports the Following synchronization modes as listed the!, indices, triggers, and so forth ) appear in WHERE clause terms limit ) expect incomplete! Columns in each result row as it sees fit it might pragma statements limited. Rows of output can appear much sooner, and if ] ] ] clause this feature is used for SQLite. Sqlite3_Soft_Heap_Limit64 ( ) API to retrieve column-names even when to disk, then... Command is a bitmask of optimizations to perform: debugging mode retrieve column-names even to. ) is not used as an index to satisfy the N instances of the middle.... Expected to survive a power outage allocated in smaller chunks on an as-needed basis direct access to sqlite3_busy_timeout )... ; Assuming there are no other `` main '' database is closed and reopened schema.auto_vacuum = each index the. Implies no limit ) large transaction ( e.g database connection optimization is attempted is very fast can... With the value 'ok ' is still true additional O ( NlogN ).! Because the left-most column of an index constraint and doing them, run pragma... But changing the SQLite environment anticipate that this pragma returns a list of SQL functions for WAL... Code that expect the incomplete behavior the default limit is -1 ( no limit ) fancy hash table to. '' and `` off '' prefix is omitted, then a query that uses an efficient database.. Parameters are the only two combinations each, resulting in 12 million iterations the.