ANALYZE — collect statistics about a database
ANALYZE [ VERBOSE ] [table_name[ (column_name[, ...] ) ] ]
   ANALYZE collects statistics about the contents
   of tables in the database, and stores the results in the pg_statistic
   system catalog.  Subsequently, the query planner uses these
   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 collected.
  
VERBOSEEnables display of progress messages.
table_nameThe name (possibly schema-qualified) of a specific table to analyze. If omitted, all regular tables, partitioned tables, and materialized views in the current database are analyzed (but not foreign tables). If the specified table is a partitioned table, both the inheritance statistics of the partitioned table as a whole and statistics of the individual partitions are updated.
column_nameThe name of a specific column to analyze. Defaults to all columns.
    When VERBOSE is specified, ANALYZE emits
    progress messages to indicate which table is currently being
    processed.  Various statistics about the tables are printed as well.
   
   Foreign tables are analyzed only when explicitly selected.  Not all
   foreign data wrappers support ANALYZE.  If the table's
   wrapper does not support ANALYZE, the command prints a
   warning and does nothing.
  
   In the default PostgreSQL configuration,
   the autovacuum daemon (see Section 24.1.6)
   takes care of automatic analyzing of tables when they are first loaded
   with data, and as they change throughout regular operation.
   When autovacuum is disabled,
   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 for read-mostly databases is to run VACUUM
   and ANALYZE once a day during a low-usage time of day.
   (This will not be sufficient if there is heavy update activity.)
  
   ANALYZE
   requires only a read lock on the target table, so it can run in
   parallel with other activity on the table.
  
   The statistics collected by ANALYZE 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 can 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 Chapter 24.
  
   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 might result
   in small changes in the planner's estimated costs shown by
   EXPLAIN.
   In rare situations, this non-determinism will cause the planner's
   choices of query plans to change after ANALYZE is run.
   To avoid this, raise the amount of statistics collected by
   ANALYZE, as described below.
  
   The extent of analysis can be controlled by adjusting the
   default_statistics_target configuration 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).
   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 100, 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 might 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.
  
   One of the values estimated by ANALYZE is the number of
   distinct values that appear in each column.  Because only a subset of the
   rows are examined, this estimate can sometimes be quite inaccurate, even
   with the largest possible statistics target.  If this inaccuracy leads to
   bad query plans, a more accurate value can be determined manually and then
   installed with
   ALTER TABLE ... ALTER COLUMN ... SET (n_distinct = ...)
   (see ALTER TABLE).
  
    If the table being analyzed has one or more children,
    ANALYZE will gather statistics twice: once on the
    rows of the parent table only, and a second time on the rows of the
    parent table with all of its children.  This second set of statistics
    is needed when planning queries that traverse the entire inheritance
    tree.  The autovacuum daemon, however, will only consider inserts or
    updates on the parent table itself when deciding whether to trigger an
    automatic analyze for that table.  If that table is rarely inserted into
    or updated, the inheritance statistics will not be up to date unless you
    run ANALYZE manually.
  
    If any of the child tables are foreign tables whose foreign data wrappers
    do not support ANALYZE, those child tables are ignored while
    gathering inheritance statistics.
  
    If the table being analyzed is completely empty, ANALYZE
    will not record new statistics for that table.  Any existing statistics
    will be retained.
  
   There is no ANALYZE statement in the SQL standard.