ANALYZE(7)							   SQL Commands 							ANALYZE(7)

NAME

       ANALYZE - collect statistics about a database

SYNOPSIS

       ANALYZE [ VERBOSE ] [ table [ (column [, ...] ) ] ]

   INPUTS
       VERBOSE
	      Enables display of progress messages.

       table  The name (possibly schema-qualified) of a specific table to analyze. Defaults to all tables in the current database.

       column The name of a specific column to analyze. Defaults to all columns.

   OUTPUTS
       ANALYZE
	      The command is complete.

DESCRIPTION

       ANALYZE collects statistics about the contents of PostgreSQL tables, and stores the results in the system table pg_statistic. Subsequently,
       the query planner uses the statistics to help determine the most efficient execution plans for queries.

       With no parameter, ANALYZE examines every table in the current database. With a parameter, ANALYZE examines only that table. It is  further
       possible to give a list of column names, in which case only the statistics for those columns are updated.

   NOTES
       It is a good idea to run ANALYZE periodically, or just after making major changes in the contents of a table. Accurate statistics will help
       the planner to choose the most appropriate query plan, and thereby improve the speed of query processing. A common strategy is to run  VAC-
       UUM [vacuum(7)] and ANALYZE once a day during a low-usage time of day.

       Unlike VACUUM FULL, ANALYZE requires only a read lock on the target table, so it can run in parallel with other activity on the table.

       For  large tables, ANALYZE takes a random sample of the table contents, rather than examining every row. This allows even very large tables
       to be analyzed in a small amount of time. Note however that the statistics are only approximate, and will change slightly each time ANALYZE
       is  run,  even  if  the	actual	table  contents did not change. This may result in small changes in the planner's estimated costs shown by
       EXPLAIN.

       The collected statistics usually include a list of some of the most common values in each column and a histogram  showing  the  approximate
       data  distribution  in  each  column. One or both of these may be omitted if ANALYZE deems them uninteresting (for example, in a unique-key
       column, there are no common values) or if the column data type does not support the appropriate operators. There is more information  about
       the statistics in the User's Guide.

       The  extent  of analysis can be controlled by adjusting the default_statistics_target parameter variable, or on a column-by-column basis by
       setting the per-column statistics target with ALTER TABLE ALTER COLUMN SET STATISTICS (see ALTER TABLE [alter_table(7)]). The target  value
       sets  the maximum number of entries in the most-common-value list and the maximum number of bins in the histogram. The default target value
       is 10, but this can be adjusted up or down to trade off accuracy of planner estimates against the time taken for ANALYZE and the amount	of
       space occupied in pg_statistic.	In particular, setting the statistics target to zero disables collection of statistics for that column. It
       may be useful to do that for columns that are never used as part of the WHERE, GROUP BY, or ORDER BY clauses of queries, since the  planner
       will have no use for statistics on such columns.

       The  largest  statistics  target  among	the  columns being analyzed determines the number of table rows sampled to prepare the statistics.
       Increasing the target causes a proportional increase in the time and space needed to do ANALYZE.

COMPATIBILITY

   SQL92
       There is no ANALYZE statement in SQL92.

SQL - Language Statements					    2002-11-22								ANALYZE(7)