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foreign_serversManual ChaptersPG1835.29. foreign_servers The view foreign_servers contains all foreign servers defined in the current database. Only those foreign servers are shown that the current user has access to (by way…foreign_servers foreign_table_optionsManual ChaptersPG1835.30. foreign_table_options The view foreign_table_options contains all the options defined for foreign tables in the current database. Only those foreign tables are shown that the current …foreign_table_options foreign_tablesManual ChaptersPG1835.31. foreign_tables The view foreign_tables contains all foreign tables defined in the current database. Only those foreign tables are shown that the current user has access to (by way of …foreign_tables formatManual ChaptersPG189.4.1. format The function format produces output formatted according to a format string, in a style similar to the C function sprintf. format(formatstr text [, formatarg "any" [, ...] ]) fo…format Formats and Format CodesManual ChaptersPG1854.1.3. Formats and Format Codes Data of a particular data type might be transmitted in any of several different formats. As of PostgreSQL 7.4 the only supported formats are “text” and “bina…Formats and Format Codes FormattingManual ChaptersPG1855.1. Formatting Source code formatting uses 4 column tab spacing, with tabs preserved (i.e., tabs are not expanded to spaces). Each logical indentation level is one additional tab stop. Lay…Formatting Free Space MapManual ChaptersPG1866.3. Free Space Map Each heap and index relation, except for hash indexes, has a Free Space Map (FSM) to keep track of available space in the relation. It's stored alongside the main relati…Free Space Map FreezingManual ChaptersPG1819.10.4. Freezing To maintain correctness even after transaction IDs wrap around, PostgreSQL marks rows that are sufficiently old as frozen. These rows are visible to everyone; other transac…Freezing FROM ClauseManual ChaptersPG18FROM Clause The FROM clause specifies one or more source tables for the SELECT. If multiple sources are specified, the result is the Cartesian product (cross join) of all the sources. But us…FROM Clause Frontend/Backend ProtocolManual ChaptersPG18Chapter 54. Frontend/Backend Protocol PostgreSQL uses a message-based protocol for communication between frontends and backends (clients and servers). The protocol is supported over TCP/IP a…Frontend/Backend Protocol Full Text SearchManual ChaptersPG18Chapter 12. Full Text SearchFull Text Search Function CallManual ChaptersPG1854.2.5. Function Call The Function Call sub-protocol allows the client to request a direct call of any function that exists in the database's pg_proc system catalog. The client must have exe…Function Call Function CallsManual ChaptersPG184.2.6. Function Calls The syntax for a function call is the name of a function (possibly qualified with a schema name), followed by its argument list enclosed in parentheses: function_name (…Function Calls Function Calls in FROMManual ChaptersPG18Function Calls in FROM PostgreSQL allows a function call to be written directly as a member of the FROM list. In the SQL standard it would be necessary to wrap such a function call in a sub-…Function Calls in FROM Function Optimization InformationManual ChaptersPG1836.11. Function Optimization Information By default, a function is just a “black box” that the database system knows very little about the behavior of. However, that means that queries using…Function Optimization Information Function OverloadingManual ChaptersPG1836.6. Function Overloading More than one function can be defined with the same SQL name, so long as the arguments they take are different. In other words, function names can be overloaded. W…Function Overloading Function SecurityManual ChaptersPG1821.6. Function Security Functions, triggers and row-level security policies allow users to insert code into the backend server that other users might execute unintentionally. Hence, these me…Function Security Function Volatility CategoriesManual ChaptersPG1836.7. Function Volatility Categories Every function has a volatility classification, with the possibilities being VOLATILE, STABLE, or IMMUTABLE. VOLATILE is the default if the CREATE FUNCTI…Function Volatility Categories Functional DependenciesManual ChaptersPG1869.2.1. Functional Dependencies Multivariate correlation can be demonstrated with a very simple data set — a table with two columns, both containing the same values: CREATE TABLE t (a INT, b…Functional Dependencies Functional DependenciesManual ChaptersPG1814.2.2.1. Functional Dependencies The simplest kind of extended statistics tracks functional dependencies, a concept used in definitions of database normal forms. We say that column b is fun…Functional Dependencies Functional DependenciesManual ChaptersPG18Functional Dependencies PostgreSQL recognizes functional dependency (allowing columns to be omitted from GROUP BY) only when a table's primary key is included in the GROUP BY list. The SQL s…Functional Dependencies FunctionsManual ChaptersPG18F.1.1. Functions bt_index_check(index regclass, heapallindexed boolean, checkunique boolean) returns void bt_index_check tests that its target, a B-Tree index, respects a variety of invarian…Functions FunctionsManual ChaptersPG18F.18.1. Functions The aggregator is an aggregate function int_array_aggregate(integer) that produces an integer array containing exactly the integers it is fed. This is a wrapper around arra…Functions FunctionsManual ChaptersPG18F.27.1. Functions pg_freespace(rel regclass IN, blkno bigint IN) returns int2 Returns the amount of free space on the page of the relation, specified by blkno, according to the FSM. pg_frees…Functions FunctionsManual ChaptersPG18F.28.1. Functions pg_get_logical_snapshot_meta(filename text) returns record # Gets logical snapshot metadata about a snapshot file that is located in the server's pg_logical/snapshots direc…Functions FunctionsManual ChaptersPG18F.30.1. Functions pg_prewarm(regclass, mode text default 'buffer', fork text default 'main', first_block int8 default null, last_block int8 default null) RETURNS int8 The first argument is t…Functions FunctionsManual ChaptersPG18F.32.3. Functions pg_stat_statements_reset(userid Oid, dbid Oid, queryid bigint, minmax_only boolean) returns timestamp with time zone pg_stat_statements_reset discards statistics gathered s…Functions FunctionsManual ChaptersPG18F.33.1. Functions pgstattuple(regclass) returns record pgstattuple returns a relation's physical length, percentage of “dead” tuples, and other info. This may help users to determine whether…Functions FunctionsManual ChaptersPG18F.34.1. Functions heap_force_kill(regclass, tid[]) returns void heap_force_kill marks “used” line pointers as “dead” without examining the tuples. The intended use of this function is to for…Functions FunctionsManual ChaptersPG18F.36.1. Functions pg_visibility_map(relation regclass, blkno bigint, all_visible OUT boolean, all_frozen OUT boolean) returns record Returns the all-visible and all-frozen bits in the visibi…Functions FunctionsManual ChaptersPG18F.38.2. Functions postgres_fdw_get_connections( IN check_conn boolean DEFAULT false, OUT server_name text, OUT user_name text, OUT valid boolean, OUT used_in_xact boolean, OUT closed boolean…Functions FunctionsManual ChaptersPG18E.6.3.4. Functions Add function casefold() to allow for more sophisticated case-insensitive matching (Jeff Davis) § This allows more accurate comparisons, i.e., a character can have multiple…Functions FunctionsManual ChaptersPG1810.3. Functions The specific function that is referenced by a function call is determined using the following procedure. Function Type Resolution Select the functions to be considered from t…Functions FunctionsManual ChaptersPG18F.48.3. Functions The unaccent() function removes accents (diacritic signs) from a given string. Basically, it's a wrapper around unaccent-type dictionaries, but it can be used outside norma…Functions Functions and OperatorsManual ChaptersPG18Chapter 9. Functions and Operators PostgreSQL provides a large number of functions and operators for the built-in data types. This chapter describes most of them, although additional special…Functions and Operators Functions and OperatorsManual ChaptersPG18F.20.3. Functions and Operators The isn module provides the standard comparison operators, plus B-tree and hash indexing support for all these data types. In addition, there are several spec…Functions and Operators Functions and OperatorsManual ChaptersPG18F.35.2. Functions and Operators The functions provided by the pg_trgm module are shown in Table F.26, the operators in Table F.27. Table F.26. pg_trgm Functions Function Description similari…Functions and Operators Functions Associated with Pipeline ModeManual ChaptersPG1832.5.2. Functions Associated with Pipeline Mode PQpipelineStatus # Returns the current pipeline mode status of the libpq connection. PGpipelineStatus PQpipelineStatus(const PGconn *conn); PQ…Functions Associated with Pipeline Mode Functions Associated with the COPY CommandManual ChaptersPG1832.10. Functions Associated with the COPY Command The COPY command in PostgreSQL has options to read from or write to the network connection used by libpq. The functions described in this se…Functions Associated with the COPY Command Functions for Producing OutputManual ChaptersPG1847.6.5. Functions for Producing Output To actually produce output, output plugins can write data to the StringInfo output buffer in ctx->out when inside the begin_cb, commit_cb, or change_cb…Functions for Producing Output