At all times, PostgreSQL maintains a write ahead log (WAL) in the pg_xlog/ subdirectory of the cluster's data directory. The log records every change made to the database's data files. This log exists primarily for crash-safety purposes: if the system crashes, the database can be restored to consistency by "replaying" the log entries made since the last checkpoint. However, the existence of the log makes it possible to use a third strategy for backing up databases: we can combine a file-system-

Value expressions are used in a variety of contexts, such as in the target list of the SELECT command, as new column values in INSERT or UPDATE, or in search conditions in a number of commands. The result of a value expression is sometimes called a scalar, to distinguish it from the result of a table expression (which is a table). Value expressions are therefore also called scalar expressions (or even simply expressions). The expression syntax allows the calculation of values from primitive par

The intagg module provides an integer aggregator and an enumerator. intagg is now obsolete, because there are built-in functions that provide a superset of its capabilities. However, the module is still provided as a compatibility wrapper around the built-in functions. F.17.1. 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 array_agg, which does the same thing for a

Name psql -- PostgreSQL interactive terminal Synopsis psql [option...] [dbname [username]] Description psql is a terminal-based front-end to PostgreSQL. It enables you to type in queries interactively, issue them to PostgreSQL, and see the query results. Alternatively, input can be from a file or from command line arguments. In addition, psql provides a number of meta-commands and various shell-like features to facilitate writing scripts and automating a wide variety of tasks. Option

Enumerated (enum) types are data types that comprise a static, ordered set of values. They are equivalent to the enum types supported in a number of programming languages. An example of an enum type might be the days of the week, or a set of status values for a piece of data. 8.7.1. Declaration of Enumerated Types Enum types are created using the CREATE TYPE command, for example: CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy'); Once created, the enum type can be used in table and function de

NameREFRESH MATERIALIZED VIEW -- replace the contents of a materialized view Synopsis REFRESH MATERIALIZED VIEW [ CONCURRENTLY ] name [ WITH [ NO ] DATA ] Description REFRESH MATERIALIZED VIEW completely replaces the contents of a materialized view. The old contents are discarded. If WITH DATA is specified (or defaults) the backing query is executed to provide the new data, and the materialized view is left in a scannable state. If WITH NO DATA is specified no new data is generate

This section describes functions that possibly return more than one row. The most widely used functions in this class are series generating functions, as detailed in Table 9-57 and Table 9-58. Other, more specialized set-returning functions are described elsewhere in this manual. See Section 7.2.1.4 for ways to combine multiple set-returning functions. Table 9-57. Series Generating Functions Function Argument Type Return Type Description generate_series(start, stop) int, bigint or numeric

NameCREATE AGGREGATE -- define a new aggregate function Synopsis CREATE AGGREGATE name ( [ argmode ] [ argname ] arg_data_type [ , ... ] ) ( SFUNC = sfunc, STYPE = state_data_type [ , SSPACE = state_data_size ] [ , FINALFUNC = ffunc ] [ , FINALFUNC_EXTRA ] [ , COMBINEFUNC = combinefunc ] [ , SERIALFUNC = serialfunc ] [ , DESERIALFUNC = deserialfunc ] [ , INITCOND = initial_condition ] [ , MSFUNC = msfunc ] [ , MINVFUNC = minvfunc ] [ , MSTYP

NameVALUES -- compute a set of rows Synopsis VALUES ( expression [, ...] ) [, ...] [ ORDER BY sort_expression [ ASC | DESC | USING operator ] [, ...] ] [ LIMIT { count | ALL } ] [ OFFSET start [ ROW | ROWS ] ] [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ] Description VALUES computes a row value or set of row values specified by value expressions. It is most commonly used to generate a "constant table" within a larger command, but it can be used on its own. W

NameALTER OPERATOR FAMILY -- change the definition of an operator family Synopsis ALTER OPERATOR FAMILY name USING index_method ADD { OPERATOR strategy_number operator_name ( op_type, op_type ) [ FOR SEARCH | FOR ORDER BY sort_family_name ] | FUNCTION support_number [ ( op_type [ , op_type ] ) ] function_name ( argument_type [, ...] ) } [, ... ] ALTER OPERATOR FAMILY name USING index_method DROP { OPERATOR strategy_number ( op_type [ , op_type ] )