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bytea Escape FormatManual ChaptersPG188.4.2. bytea Escape Format The “escape” format is the traditional PostgreSQL format for the bytea type. It takes the approach of representing a binary string as a sequence of ASCII character…bytea Escape Format bytea Hex FormatManual ChaptersPG188.4.1. bytea Hex Format The “hex” format encodes binary data as 2 hexadecimal digits per byte, most significant nibble first. The entire string is preceded by the sequence \x (to distinguish…bytea Hex Format C++ Application Development with External C ModuleManual ChaptersPG1834.13.2. C++ Application Development with External C Module If you understand these technical limitations of the ecpg preprocessor in C++, you might come to the conclusion that linking C obj…C++ Application Development with External C Module C++ ApplicationsManual ChaptersPG1834.13. C++ Applications ECPG has some limited support for C++ applications. This section describes some caveats. The ecpg preprocessor takes an input file written in C (or something like C) …C++ Applications C-Language FunctionsManual ChaptersPG1836.10. C-Language Functions User-defined functions can be written in C (or a language that can be made compatible with C, such as C++). Such functions are compiled into dynamically loadable …C-Language Functions CALLManual ChaptersPG18CALL CALL — invoke a procedure Synopsis CALL name ( [ argument ] [, ...] )CALL Calling a ProcedureManual ChaptersPG1841.6.3. Calling a Procedure A PL/pgSQL function, procedure, or DO block can call a procedure using CALL. Output parameters are handled differently from the way that CALL works in plain SQL. …Calling a Procedure Calling FunctionsManual ChaptersPG184.3. Calling Functions PostgreSQL allows functions that have named parameters to be called using either positional or named notation. Named notation is especially useful for functions that h…Calling Functions Canceling Queries in ProgressManual ChaptersPG1832.7. Canceling Queries in ProgressCanceling Queries in Progress Canceling Requests in ProgressManual ChaptersPG1854.2.8. Canceling Requests in Progress During the processing of a query, the frontend might request cancellation of the query. The cancel request is not sent directly on the open connection …Canceling Requests in Progress Cannot Pass Named Parameters to QueriesManual ChaptersPG18D.3.2.2. Cannot Pass Named Parameters to Queries The XPath-based functions support passing one parameter to serve as the XPath expression's context item, but do not support passing additiona…Cannot Pass Named Parameters to Queries CapabilitiesManual ChaptersPG1847.6.2. Capabilities To decode, format and output changes, output plugins can use most of the backend's normal infrastructure, including calling output functions. Read only access to relatio…Capabilities Capturing Changes at Command EndManual ChaptersPG189.30.1. Capturing Changes at Command End pg_event_trigger_ddl_commands () → setof record pg_event_trigger_ddl_commands returns a list of DDL commands executed by each user action, when invok…Capturing Changes at Command End Cascading ReplicationManual ChaptersPG1826.2.7. Cascading Replication The cascading replication feature allows a standby server to accept replication connections and stream WAL records to other standbys, acting as a relay. This ca…Cascading Replication CASEManual ChaptersPG189.18.1. CASE The SQL CASE expression is a generic conditional expression, similar to if/else statements in other programming languages: CASE WHEN condition THEN result [WHEN ...] [ELSE resul…CASE CastsManual ChaptersPG18F.20.2. Casts The isn module provides the following pairs of type casts: ISBN13 <=> EAN13 ISMN13 <=> EAN13 ISSN13 <=> EAN13 ISBN <=> EAN13 ISMN <=> EAN13 ISSN <=> EAN13 UPC <=> EAN13 ISBN <=…Casts CaveatsManual ChaptersPG1825.3.8. Caveats At this writing, there are several limitations of the continuous archiving technique. These will probably be fixed in future releases: If a CREATE DATABASE command is execute…Caveats CaveatsManual ChaptersPG185.11.1. Caveats Note that not all SQL commands are able to work on inheritance hierarchies. Commands that are used for data querying, data modification, or schema modification (e.g., SELECT,…Caveats CaveatsManual ChaptersPG185.12.3.3. Caveats The following caveats apply to partitioning implemented using inheritance: There is no automatic way to verify that all of the CHECK constraints are mutually exclusive. It …Caveats CaveatsManual ChaptersPG1826.4.5. Caveats There are several limitations of hot standby. These can and probably will be fixed in future releases: Full knowledge of running transactions is required before snapshots can…Caveats CaveatsManual ChaptersPG1847.8.2. Caveats In synchronous replication setup, a deadlock can happen, if the transaction has locked [user] catalog tables exclusively. See Section 47.6.2 for information on user catalog t…Caveats CaveatsManual ChaptersPG1813.6. Caveats Some DDL commands, currently only TRUNCATE and the table-rewriting forms of ALTER TABLE, are not MVCC-safe. This means that after the truncation or rewrite commits, the table w…Caveats CaveatsManual ChaptersPG1814.1.3. Caveats There are two significant ways in which run times measured by EXPLAIN ANALYZE can deviate from normal execution of the same query. First, since no output rows are delivered t…Caveats Certificate AuthenticationManual ChaptersPG1820.12. Certificate Authentication This authentication method uses SSL client certificates to perform authentication. It is therefore only available for SSL connections; see Section 18.9.2 fo…Certificate Authentication Change CallbackManual ChaptersPG1847.6.4.5. Change Callback The required change_cb callback is called for every individual row modification inside a transaction, may it be an INSERT, UPDATE, or DELETE. Even if the original c…Change Callback ChangesManual ChaptersPG18E.5.2. Changes Check for CREATE privileges on the schema in CREATE STATISTICS (Jelte Fennema-Nio) § This omission allowed table owners to create statistics in any schema, potentially leading…Changes ChangesManual ChaptersPG18E.4.2. Changes Guard against unexpected dimensions of oidvector/int2vector (Tom Lane) § These data types are expected to be 1-dimensional arrays containing no nulls, but there are cast pathw…Changes ChangesManual ChaptersPG18E.3.2. Changes Fix failure after replaying a multixid truncation record from WAL that was generated by an older minor version (Heikki Linnakangas) § Erroneous logic for coping with the way t…Changes ChangesManual ChaptersPG18E.2.2. Changes Prevent unbounded recursion while processing startup packets (Michael Paquier) § A malicious client could crash the connected backend by alternating rejected SSL and GSS encry…Changes ChangesManual ChaptersPG18E.1.2. Changes Restrict logical decoding output plugins to the set specified by a new server parameter output_plugin_libraries (Jacob Champion) § § Previously, a replication user could selec…Changes ChangesManual ChaptersPG18E.6.3. Changes Below you will find a detailed account of the changes between PostgreSQL 18 and the previous major release.Changes Changing a Column's Data TypeManual ChaptersPG185.7.6. Changing a Column's Data Type To convert a column to a different data type, use a command like: ALTER TABLE products ALTER COLUMN price TYPE numeric(10,2); This will succeed only if e…Changing a Column's Data Type Changing a Column's Default ValueManual ChaptersPG185.7.5. Changing a Column's Default Value To set a new default for a column, use a command like: ALTER TABLE products ALTER COLUMN price SET DEFAULT 7.77; Note that this doesn't affect any ex…Changing a Column's Default Value Changing Time SourcesManual ChaptersPG18Changing Time Sources On some newer Linux systems, it's possible to change the clock source used to collect timing data at any time. A second example shows the slowdown possible from switchi…Changing Time Sources Character Set SupportManual ChaptersPG1823.3. Character Set Support The character set support in PostgreSQL allows you to store text in a variety of character sets (also called encodings), including single-byte character sets such…Character Set Support Character StringsManual ChaptersPG1834.6.1. Character Strings Some functions such as PGTYPESnumeric_to_asc return a pointer to a freshly allocated character string. These results should be freed with PGTYPESchar_free instead o…Character Strings Character TypesManual ChaptersPG188.3. Character Types Table 8.4. Character Types Name Description character varying(n), varchar(n) variable-length with limit character(n), char(n), bpchar(n) fixed-length, blank-padded bpcha…Character Types character_setsManual ChaptersPG1835.7. character_sets The view character_sets identifies the character sets available in the current database. Since PostgreSQL does not support multiple character sets within one database, t…character_sets Check CallbackManual ChaptersPG1849.2.2. Check Callback The check_configured_cb callback is called to determine whether the module is fully configured and ready to accept WAL files (e.g., its configuration parameters are se…Check Callback Check ConstraintsManual ChaptersPG185.5.1. Check Constraints A check constraint is the most generic constraint type. It allows you to specify that the value in a certain column must satisfy a Boolean (truth-value) expression. …Check Constraints