Provided by: postgresql-client-8.4_8.4.8-2_i386 bug

NAME

       SELECT, TABLE, WITH - retrieve rows from a table or view

SYNOPSIS

       [ WITH [ RECURSIVE ] with_query [, ...] ]
       SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
           * | expression [ [ AS ] output_name ] [, ...]
           [ FROM from_item [, ...] ]
           [ WHERE condition ]
           [ GROUP BY expression [, ...] ]
           [ HAVING condition [, ...] ]
           [ WINDOW window_name AS ( window_definition ) [, ...] ]
           [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]
           [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ]
           [ LIMIT { count | ALL } ]
           [ OFFSET start [ ROW | ROWS ] ]
           [ FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY ]
           [ FOR { UPDATE | SHARE } [ OF table_name [, ...] ] [ NOWAIT ] [...] ]

       where from_item can be one of:

           [ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
           ( select ) [ AS ] alias [ ( column_alias [, ...] ) ]
           with_query_name [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
           function_name ( [ argument [, ...] ] ) [ AS ] alias [ ( column_alias [, ...] | column_definition [, ...] ) ]
           function_name ( [ argument [, ...] ] ) AS ( column_definition [, ...] )
           from_item [ NATURAL ] join_type from_item [ ON join_condition | USING ( join_column [, ...] ) ]

       and with_query is:

           with_query_name [ ( column_name [, ...] ) ] AS ( select )

       TABLE { [ ONLY ] table_name [ * ] | with_query_name }

DESCRIPTION

       SELECT retrieves rows from zero or more tables.  The general processing
       of SELECT is as follows:

       1.     All queries in the WITH list are  computed.   These  effectively
              serve  as  temporary  tables  that can be referenced in the FROM
              list. A WITH query that is referenced more than once in FROM  is
              computed only once.  (See WITH Clause [select(7)] below.)

       2.     All  elements  in  the FROM list are computed.  (Each element in
              the FROM list is a real or virtual  table.)  If  more  than  one
              element  is  specified  in  the FROM list, they are cross-joined
              together.  (See FROM Clause [select(7)] below.)

       3.     If the WHERE clause is specified, all rows that do  not  satisfy
              the  condition are eliminated from the output. (See WHERE Clause
              [select(7)] below.)

       4.     If the GROUP BY clause is specified, the output is divided  into
              groups  of  rows that match on one or more values. If the HAVING
              clause is present, it eliminates groups that do not satisfy  the
              given  condition.  (See  GROUP  BY Clause [select(7)] and HAVING
              Clause [select(7)] below.)

       5.     The actual output rows are  computed  using  the  SELECT  output
              expressions  for each selected row. (See SELECT List [select(7)]
              below.)

       6.     Using the operators UNION, INTERSECT, and EXCEPT, the output  of
              more  than one SELECT statement can be combined to form a single
              result set. The UNION operator returns all rows that are in  one
              or  both  of the result sets. The INTERSECT operator returns all
              rows that are strictly in both result sets. The EXCEPT  operator
              returns the rows that are in the first result set but not in the
              second. In all three cases, duplicate rows are eliminated unless
              ALL  is  specified.  (See  UNION  Clause  [select(7)], INTERSECT
              Clause [select(7)], and EXCEPT Clause [select(7)] below.)

       7.     If the ORDER BY clause  is  specified,  the  returned  rows  are
              sorted  in  the  specified  order. If ORDER BY is not given, the
              rows are returned in whatever order the system finds fastest  to
              produce. (See ORDER BY Clause [select(7)] below.)

       8.     DISTINCT  eliminates duplicate rows from the result. DISTINCT ON
              eliminates rows that match on all the specified expressions. ALL
              (the   default)   will  return  all  candidate  rows,  including
              duplicates. (See DISTINCT Clause [select(7)] below.)

       9.     If the LIMIT (or FETCH FIRST) or OFFSET clause is specified, the
              SELECT  statement only returns a subset of the result rows. (See
              LIMIT Clause [select(7)] below.)

       10.    If FOR UPDATE or FOR SHARE is specified,  the  SELECT  statement
              locks  the  selected  rows  against concurrent updates. (See FOR
              UPDATE/FOR SHARE Clause [select(7)] below.)

       You must have SELECT privilege on each column used in a SELECT command.
       The  use  of  FOR UPDATE or FOR SHARE requires UPDATE privilege as well
       (for at least one column of each table so selected).

PARAMETERS

   WITH CLAUSE
       The WITH clause allows you to specify one or more subqueries  that  can
       be referenced by name in the primary query.  The subqueries effectively
       act as temporary tables or views for the duration of the primary query.

       A name (without schema qualification) must be specified for  each  WITH
       query.  Optionally, a list of column names can be specified; if this is
       omitted, the column names are inferred from the subquery.

       If RECURSIVE is specified, it allows a subquery to reference itself  by
       name. Such a subquery must have the form

       non_recursive_term UNION [ ALL ] recursive_term

       where  the  recursive self-reference must appear on the right-hand side
       of the UNION. Only one recursive self-reference is permitted per query.

       Another effect of RECURSIVE is that WITH queries need not be ordered: a
       query  can  reference  another one that is later in the list. (However,
       circular  references,  or  mutual  recursion,  are  not   implemented.)
       Without RECURSIVE, WITH queries can only reference sibling WITH queries
       that are earlier in the WITH list.

       A useful property of WITH queries is that they are evaluated only  once
       per execution of the primary query, even if the primary query refers to
       them more than once.

       See in the documentation for additional information.

   FROM 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 usually  qualification  conditions
       are  added  to  restrict  the  returned  rows  to a small subset of the
       Cartesian product.

       The FROM clause can contain the following elements:

       table_name
              The name (optionally schema-qualified) of an existing  table  or
              view.  If ONLY is specified, only that table is scanned. If ONLY
              is not specified,  the  table  and  any  descendant  tables  are
              scanned.

       alias  A  substitute  name  for  the FROM item containing the alias. An
              alias is used for brevity or to eliminate  ambiguity  for  self-
              joins  (where the same table is scanned multiple times). When an
              alias is provided, it completely hides the actual  name  of  the
              table  or  function;  for  example  given  FROM  foo  AS  f, the
              remainder of the SELECT must refer to this FROM item  as  f  not
              foo.  If  an  alias  is written, a column alias list can also be
              written to provide substitute names for one or more  columns  of
              the table.

       select A  sub-SELECT can appear in the FROM clause. This acts as though
              its output were created as a temporary table for the duration of
              this  single  SELECT  command.  Note that the sub-SELECT must be
              surrounded by parentheses, and an alias must be provided for it.
              A VALUES [values(7)] command can also be used here.

       with_query_name
              A  WITH  query is referenced by writing its name, just as though
              the query's name were a table name. (In  fact,  the  WITH  query
              hides  any  real  table of the same name for the purposes of the
              primary query. If necessary, you can refer to a  real  table  of
              the  same name by schema-qualifying the table's name.)  An alias
              can be provided in the same way as for a table.

       function_name
              Function  calls  can  appear  in  the  FROM  clause.  (This   is
              especially useful for functions that return result sets, but any
              function can be used.) This  acts  as  though  its  output  were
              created  as  a  temporary  table for the duration of this single
              SELECT command. An alias can  also  be  used.  If  an  alias  is
              written,  a  column  alias  list  can also be written to provide
              substitute names for one or more attributes  of  the  function's
              composite  return  type.  If  the  function  has been defined as
              returning the record data type, then an alias or the key word AS
              must  be  present,  followed  by a column definition list in the
              form ( column_name data_type [, ... ] ). The  column  definition
              list  must match the actual number and types of columns returned
              by the function.

       join_type
              One of

              o [ INNER ] JOIN

              o LEFT [ OUTER ] JOIN

              o RIGHT [ OUTER ] JOIN

              o FULL [ OUTER ] JOIN

              o CROSS JOIN

       For the INNER and OUTER join types, a join condition must be specified,
       namely exactly one of NATURAL, ON join_condition, or USING (join_column
       [, ...]).  See below for the meaning. For CROSS  JOIN,  none  of  these
       clauses can appear.

       A  JOIN clause combines two FROM items. Use parentheses if necessary to
       determine the order of nesting. In the absence  of  parentheses,  JOINs
       nest left-to-right. In any case JOIN binds more tightly than the commas
       separating FROM items.

       CROSS JOIN and INNER JOIN produce a simple Cartesian product, the  same
       result  as you get from listing the two items at the top level of FROM,
       but  restricted  by  the  join  condition  (if  any).   CROSS  JOIN  is
       equivalent  to  INNER  JOIN  ON (TRUE), that is, no rows are removed by
       qualification.  These join types are  just  a  notational  convenience,
       since they do nothing you couldn't do with plain FROM and WHERE.

       LEFT  OUTER  JOIN  returns  all rows in the qualified Cartesian product
       (i.e., all combined rows that pass its join condition), plus  one  copy
       of  each  row  in the left-hand table for which there was no right-hand
       row that passed the join condition. This left-hand row is  extended  to
       the  full  width  of  the joined table by inserting null values for the
       right-hand columns. Note that only the JOIN clause's own  condition  is
       considered while deciding which rows have matches. Outer conditions are
       applied afterwards.

       Conversely, RIGHT OUTER JOIN returns all the joined rows, plus one  row
       for  each  unmatched  right-hand row (extended with nulls on the left).
       This is just a notational convenience, since you could convert it to  a
       LEFT OUTER JOIN by switching the left and right inputs.

       FULL  OUTER  JOIN  returns  all  the joined rows, plus one row for each
       unmatched left-hand row (extended with nulls on the  right),  plus  one
       row  for  each  unmatched  right-hand  row  (extended with nulls on the
       left).

       ON join_condition
              join_condition is an expression resulting in  a  value  of  type
              boolean (similar to a WHERE clause) that specifies which rows in
              a join are considered to match.

       USING ( join_column [, ...] )
              A clause of the form USING ( a, b, ... )  is  shorthand  for  ON
              left_table.a  =  right_table.a  AND left_table.b = right_table.b
              ....  Also,  USING  implies  that  only  one  of  each  pair  of
              equivalent  columns  will  be  included  in the join output, not
              both.

       NATURAL
              NATURAL is shorthand for a USING list that mentions all  columns
              in the two tables that have the same names.

   WHERE CLAUSE
       The optional WHERE clause has the general form

       WHERE condition

       where  condition  is  any expression that evaluates to a result of type
       boolean.  Any  row  that  does  not  satisfy  this  condition  will  be
       eliminated from the output. A row satisfies the condition if it returns
       true when the actual  row  values  are  substituted  for  any  variable
       references.

   GROUP BY CLAUSE
       The optional GROUP BY clause has the general form

       GROUP BY expression [, ...]

       GROUP  BY  will condense into a single row all selected rows that share
       the same values for the grouped expressions. expression can be an input
       column  name, or the name or ordinal number of an output column (SELECT
       list item), or an arbitrary expression formed from input-column values.
       In  case of ambiguity, a GROUP BY name will be interpreted as an input-
       column name rather than an output column name.

       Aggregate functions, if any are used,  are  computed  across  all  rows
       making  up  each  group,  producing  a  separate  value  for each group
       (whereas without  GROUP  BY,  an  aggregate  produces  a  single  value
       computed  across  all the selected rows).  When GROUP BY is present, it
       is not valid for the SELECT list  expressions  to  refer  to  ungrouped
       columns  except  within  aggregate functions, since there would be more
       than one possible value to return for an ungrouped column.

   HAVING CLAUSE
       The optional HAVING clause has the general form

       HAVING condition

       where condition is the same as specified for the WHERE clause.

       HAVING eliminates group rows that do not satisfy the condition.  HAVING
       is  different  from  WHERE:  WHERE  filters  individual rows before the
       application of GROUP BY, while HAVING filters  group  rows  created  by
       GROUP  BY.  Each  column  referenced  in  condition  must unambiguously
       reference a grouping column, unless the  reference  appears  within  an
       aggregate function.

       The presence of HAVING turns a query into a grouped query even if there
       is no GROUP BY clause. This is the same as what happens when the  query
       contains  aggregate  functions but no GROUP BY clause. All the selected
       rows are considered to form a single group, and  the  SELECT  list  and
       HAVING  clause  can  only reference table columns from within aggregate
       functions. Such a query will emit a single row if the HAVING  condition
       is true, zero rows if it is not true.

   WINDOW CLAUSE
       The optional WINDOW clause has the general form

       WINDOW window_name AS ( window_definition ) [, ...]

       where  window_name  is  a  name  that can be referenced from subsequent
       window definitions or OVER clauses, and window_definition is

       [ existing_window_name ]
       [ PARTITION BY expression [, ...] ]
       [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ]
       [ frame_clause ]

       If an existing_window_name is specified it must  refer  to  an  earlier
       entry in the WINDOW list; the new window copies its partitioning clause
       from that entry, as well as its ordering clause if any.  In  this  case
       the  new  window cannot specify its own PARTITION BY clause, and it can
       specify ORDER BY only if the copied window does not have one.  The  new
       window  always  uses  its  own frame clause; the copied window must not
       specify a frame clause.

       The elements of the PARTITION BY list are interpreted in much the  same
       fashion  as elements of a GROUP BY Clause [select(7)], except that they
       are always simple expressions and never the name or number of an output
       column.   Another  difference  is  that  these  expressions can contain
       aggregate function calls, which are not allowed in a regular  GROUP  BY
       clause.  They  are allowed here because windowing occurs after grouping
       and aggregation.

       Similarly, the elements of the ORDER BY list are  interpreted  in  much
       the  same fashion as elements of an ORDER BY Clause [select(7)], except
       that the expressions are always taken as simple expressions  and  never
       the name or number of an output column.

       The optional frame_clause defines the window frame for window functions
       that depend on the frame (not all do). It can be one of

       RANGE UNBOUNDED PRECEDING
       RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
       RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING
       ROWS UNBOUNDED PRECEDING
       ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW
       ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING

       The first two are equivalent and are also the  default:  they  set  the
       frame  to  be  all rows from the partition start up through the current
       row's last peer in the ORDER BY ordering (which means all rows if there
       is  no  ORDER  BY).  The  options RANGE BETWEEN UNBOUNDED PRECEDING AND
       UNBOUNDED FOLLOWING and ROWS BETWEEN UNBOUNDED PRECEDING AND  UNBOUNDED
       FOLLOWING  are  also  equivalent:  they  always  select all rows in the
       partition.  Lastly, ROWS UNBOUNDED PRECEDING or its verbose  equivalent
       ROWS  BETWEEN  UNBOUNDED  PRECEDING  AND CURRENT ROW select all rows up
       through the current row (regardless of duplicates).  Beware  that  this
       option  can  produce  implementation-dependent  results if the ORDER BY
       ordering does not order the rows uniquely.

       The purpose of a WINDOW clause is to specify  the  behavior  of  window
       functions  appearing in the query's SELECT List [select(7)] or ORDER BY
       Clause [select(7)]. These functions can  reference  the  WINDOW  clause
       entries  by  name in their OVER clauses. A WINDOW clause entry does not
       have to be referenced anywhere, however; if it is not used in the query
       it  is  simply  ignored. It is possible to use window functions without
       any WINDOW clause at all, since a window function call can specify  its
       window  definition  directly  in  its  OVER clause. However, the WINDOW
       clause saves typing when the same window definition is needed for  more
       than one window function.

       Window  functions  are  described in detail in in the documentation, in
       the documentation, and in the documentation.

   SELECT LIST
       The SELECT list (between the  key  words  SELECT  and  FROM)  specifies
       expressions  that  form  the  output  rows of the SELECT statement. The
       expressions can (and usually do) refer to columns computed in the  FROM
       clause.

       Just  as  in  a table, every output column of a SELECT has a name. In a
       simple SELECT this name is just used to label the column  for  display,
       but  when the SELECT is a sub-query of a larger query, the name is seen
       by the larger query as the column name of the virtual table produced by
       the  sub-query.  To specify the name to use for an output column, write
       AS output_name after the column's expression. (You  can  omit  AS,  but
       only  if  the desired output name does not match any PostgreSQL keyword
       (see in the documentation).  For  protection  against  possible  future
       keyword additions, it is recommended that you always either write AS or
       double-quote the output name.)  If you do not specify a column name,  a
       name  is chosen automatically by PostgreSQL. If the column's expression
       is a simple column reference then the chosen name is the same  as  that
       column's  name;  in  more  complex  cases a generated name looking like
       ?columnN? is usually chosen.

       An output column's name can be used to refer to the column's  value  in
       ORDER  BY and GROUP BY clauses, but not in the WHERE or HAVING clauses;
       there you must write out the expression instead.

       Instead of an expression, * can be written in  the  output  list  as  a
       shorthand for all the columns of the selected rows. Also, you can write
       table_name.* as a shorthand for  the  columns  coming  from  just  that
       table.  In these cases it is not possible to specify new names with AS;
       the output column names will be the same as the table columns' names.

   UNION CLAUSE
       The UNION clause has this general form:

       select_statement UNION [ ALL ] select_statement

       select_statement is any SELECT statement without an  ORDER  BY,  LIMIT,
       FOR  UPDATE,  or FOR SHARE clause.  (ORDER BY and LIMIT can be attached
       to  a  subexpression  if  it  is  enclosed  in   parentheses.   Without
       parentheses,  these clauses will be taken to apply to the result of the
       UNION, not to its right-hand input expression.)

       The UNION operator computes the set union of the rows returned  by  the
       involved  SELECT  statements.  A  row is in the set union of two result
       sets if it appears in at least one of the result sets. The  two  SELECT
       statements that represent the direct operands of the UNION must produce
       the same number of  columns,  and  corresponding  columns  must  be  of
       compatible data types.

       The  result of UNION does not contain any duplicate rows unless the ALL
       option  is  specified.   ALL  prevents   elimination   of   duplicates.
       (Therefore,  UNION ALL is usually significantly quicker than UNION; use
       ALL when you can.)

       Multiple UNION operators in the same  SELECT  statement  are  evaluated
       left to right, unless otherwise indicated by parentheses.

       Currently,  FOR  UPDATE  and FOR SHARE cannot be specified either for a
       UNION result or for any input of a UNION.

   INTERSECT CLAUSE
       The INTERSECT clause has this general form:

       select_statement INTERSECT [ ALL ] select_statement

       select_statement is any SELECT statement without an  ORDER  BY,  LIMIT,
       FOR UPDATE, or FOR SHARE clause.

       The  INTERSECT  operator  computes  the  set  intersection  of the rows
       returned  by  the  involved  SELECT  statements.  A  row  is   in   the
       intersection of two result sets if it appears in both result sets.

       The  result of INTERSECT does not contain any duplicate rows unless the
       ALL option is specified.  With ALL, a row that has m duplicates in  the
       left  table  and  n  duplicates in the right table will appear min(m,n)
       times in the result set.

       Multiple INTERSECT operators in the same SELECT statement are evaluated
       left  to  right, unless parentheses dictate otherwise.  INTERSECT binds
       more tightly than UNION. That is, A UNION B INTERSECT C will be read as
       A UNION (B INTERSECT C).

       Currently,  FOR  UPDATE and FOR SHARE cannot be specified either for an
       INTERSECT result or for any input of an INTERSECT.

   EXCEPT CLAUSE
       The EXCEPT clause has this general form:

       select_statement EXCEPT [ ALL ] select_statement

       select_statement is any SELECT statement without an  ORDER  BY,  LIMIT,
       FOR UPDATE, or FOR SHARE clause.

       The  EXCEPT operator computes the set of rows that are in the result of
       the left SELECT statement but not in the result of the right one.

       The result of EXCEPT does not contain any duplicate rows unless the ALL
       option is specified.  With ALL, a row that has m duplicates in the left
       table and n duplicates in the right table will appear max(m-n,0)  times
       in the result set.

       Multiple  EXCEPT  operators  in the same SELECT statement are evaluated
       left to right, unless parentheses dictate otherwise.  EXCEPT  binds  at
       the same level as UNION.

       Currently,  FOR  UPDATE and FOR SHARE cannot be specified either for an
       EXCEPT result or for any input of an EXCEPT.

   ORDER BY CLAUSE
       The optional ORDER BY clause has this general form:

       ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...]

       The ORDER BY clause causes the result rows to be  sorted  according  to
       the  specified  expression(s).  If  two rows are equal according to the
       leftmost expression, they are compared according to the next expression
       and  so  on.  If they are equal according to all specified expressions,
       they are returned in an implementation-dependent order.

       Each expression can be the name or ordinal number of an  output  column
       (SELECT  list  item),  or it can be an arbitrary expression formed from
       input-column values.

       The ordinal number refers to the ordinal  (left-to-right)  position  of
       the output column. This feature makes it possible to define an ordering
       on the basis of a column that does not have  a  unique  name.  This  is
       never  absolutely  necessary  because it is always possible to assign a
       name to an output column using the AS clause.

       It is also possible to  use  arbitrary  expressions  in  the  ORDER  BY
       clause, including columns that do not appear in the SELECT output list.
       Thus the following statement is valid:

       SELECT name FROM distributors ORDER BY code;

       A limitation of this feature is that an ORDER BY clause applying to the
       result  of  a  UNION,  INTERSECT,  or EXCEPT clause can only specify an
       output column name or number, not an expression.

       If an ORDER BY expression is a simple name that matches both an  output
       column name and an input column name, ORDER BY will interpret it as the
       output column name.  This is the opposite of the choice that  GROUP  BY
       will  make  in  the  same  situation.  This inconsistency is made to be
       compatible with the SQL standard.

       Optionally  one  can  add  the  key  word  ASC  (ascending)   or   DESC
       (descending)  after  any  expression  in  the  ORDER  BY clause. If not
       specified,  ASC  is  assumed  by  default.  Alternatively,  a  specific
       ordering  operator  name  can  be  specified  in  the USING clause.  An
       ordering operator must be a less-than or greater-than member of some B-
       tree operator family.  ASC is usually equivalent to USING < and DESC is
       usually equivalent to USING >.  (But the creator of a user-defined data
       type can define exactly what the default sort ordering is, and it might
       correspond to operators with other names.)

       If NULLS LAST is specified, null values sort after all non-null values;
       if  NULLS  FIRST  is  specified,  null  values sort before all non-null
       values. If neither is specified, the default  behavior  is  NULLS  LAST
       when  ASC  is  specified  or  implied,  and  NULLS  FIRST  when DESC is
       specified (thus, the default is to act as though nulls are larger  than
       non-nulls).   When  USING  is  specified,  the  default  nulls ordering
       depends  on  whether  the  operator  is  a  less-than  or  greater-than
       operator.

       Note  that  ordering  options apply only to the expression they follow;
       for example ORDER BY x, y DESC does not mean the same thing as ORDER BY
       x DESC, y DESC.

       Character-string  data  is  sorted  according  to  the  locale-specific
       collation order that was established when the database was created.

   DISTINCT CLAUSE
       If DISTINCT is specified, all  duplicate  rows  are  removed  from  the
       result  set  (one  row  is  kept  from  each  group of duplicates). ALL
       specifies the opposite: all rows are kept; that is the default.

       DISTINCT ON ( expression [, ...] ) keeps only the first row of each set
       of  rows where the given expressions evaluate to equal. The DISTINCT ON
       expressions are interpreted using the same rules as for ORDER  BY  (see
       above). Note that the ``first row'' of each set is unpredictable unless
       ORDER BY is used to ensure that the  desired  row  appears  first.  For
       example:

       SELECT DISTINCT ON (location) location, time, report
           FROM weather_reports
           ORDER BY location, time DESC;

       retrieves  the  most recent weather report for each location. But if we
       had not used ORDER BY to force descending order of time values for each
       location, we'd have gotten a report from an unpredictable time for each
       location.

       The  DISTINCT  ON  expression(s)  must  match  the  leftmost  ORDER  BY
       expression(s).  The  ORDER  BY  clause will normally contain additional
       expression(s) that determine the desired precedence of rows within each
       DISTINCT ON group.

   LIMIT CLAUSE
       The LIMIT clause consists of two independent sub-clauses:

       LIMIT { count | ALL }
       OFFSET start

       count  specifies  the  maximum  number  of  rows to return, while start
       specifies the number of rows to skip before starting  to  return  rows.
       When  both  are  specified,  start  rows are skipped before starting to
       count the count rows to be returned.

       If the count expression evaluates to NULL, it is treated as LIMIT  ALL,
       i.e.,  no  limit. If start evaluates to NULL, it is treated the same as
       OFFSET 0.

       SQL:2008 introduced a different syntax to achieve the same thing, which
       PostgreSQL also supports. It is:

       OFFSET start { ROW | ROWS }
       FETCH { FIRST | NEXT } [ count ] { ROW | ROWS } ONLY

       Both  clauses  are optional, but if present the OFFSET clause must come
       before the FETCH clause. ROW and ROWS as well as  FIRST  and  NEXT  are
       noise  words that don't influence the effects of these clauses. In this
       syntax, when using expressions other than simple constants for start or
       count, parentheses will be necessary in most cases. If count is omitted
       in FETCH, it defaults to 1.

       When using LIMIT, it is a good idea to use  an  ORDER  BY  clause  that
       constrains  the result rows into a unique order. Otherwise you will get
       an unpredictable subset of the query's rows -- you might be asking  for
       the  tenth  through twentieth rows, but tenth through twentieth in what
       ordering? You don't know what ordering unless you specify ORDER BY.

       The query planner takes LIMIT into  account  when  generating  a  query
       plan, so you are very likely to get different plans (yielding different
       row orders) depending on what you use for LIMIT and OFFSET. Thus, using
       different  LIMIT/OFFSET  values  to select different subsets of a query
       result will give inconsistent results unless you enforce a  predictable
       result  ordering  with  ORDER  BY. This is not a bug; it is an inherent
       consequence of the fact that  SQL  does  not  promise  to  deliver  the
       results  of  a query in any particular order unless ORDER BY is used to
       constrain the order.

       It is even possible for repeated executions of the same LIMIT query  to
       return  different  subsets  of  the rows of a table, if there is not an
       ORDER BY to enforce selection of a deterministic subset. Again, this is
       not  a bug; determinism of the results is simply not guaranteed in such
       a case.

   FOR UPDATE/FOR SHARE CLAUSE
       The FOR UPDATE clause has this form:

       FOR UPDATE [ OF table_name [, ...] ] [ NOWAIT ]

       The closely related FOR SHARE clause has this form:

       FOR SHARE [ OF table_name [, ...] ] [ NOWAIT ]

       FOR UPDATE causes the rows retrieved by  the  SELECT  statement  to  be
       locked  as though for update. This prevents them from being modified or
       deleted by other transactions until the current transaction ends.  That
       is,  other  transactions  that  attempt  UPDATE,  DELETE, or SELECT FOR
       UPDATE of these rows will be  blocked  until  the  current  transaction
       ends.   Also,  if  an UPDATE, DELETE, or SELECT FOR UPDATE from another
       transaction has already locked a  selected  row  or  rows,  SELECT  FOR
       UPDATE  will  wait for the other transaction to complete, and will then
       lock and return the updated row (or no row, if the  row  was  deleted).
       For further discussion see in the documentation.

       To prevent the operation from waiting for other transactions to commit,
       use the NOWAIT option. SELECT  FOR  UPDATE  NOWAIT  reports  an  error,
       rather  than  waiting,  if a selected row cannot be locked immediately.
       Note that NOWAIT applies only to the row-level lock(s) -- the  required
       ROW  SHARE  table-level lock is still taken in the ordinary way (see in
       the documentation). You can use the NOWAIT option of LOCK [lock(7)]  if
       you need to acquire the table-level lock without waiting.

       FOR  SHARE  behaves  similarly, except that it acquires a shared rather
       than exclusive lock on each retrieved row. A shared lock  blocks  other
       transactions  from  performing  UPDATE, DELETE, or SELECT FOR UPDATE on
       these rows, but it does not prevent them  from  performing  SELECT  FOR
       SHARE.

       If specific tables are named in FOR UPDATE or FOR SHARE, then only rows
       coming from those tables are locked;  any  other  tables  used  in  the
       SELECT  are  simply  read  as  usual.  A FOR UPDATE or FOR SHARE clause
       without a table list affects all tables used in the  command.   If  FOR
       UPDATE  or  FOR SHARE is applied to a view or sub-query, it affects all
       tables used in the view or sub-query.  However, FOR UPDATE/FOR SHARE do
       not apply to WITH queries referenced by the primary query.  If you want
       row locking to occur within a WITH query, specify  FOR  UPDATE  or  FOR
       SHARE within the WITH query.

       Multiple  FOR  UPDATE  and  FOR  SHARE  clauses can be written if it is
       necessary to specify different locking behavior for  different  tables.
       If  the  same  table  is mentioned (or implicitly affected) by both FOR
       UPDATE and FOR SHARE clauses, then  it  is  processed  as  FOR  UPDATE.
       Similarly,  a  table is processed as NOWAIT if that is specified in any
       of the clauses affecting it.

       FOR UPDATE and FOR SHARE cannot be used in contexts where returned rows
       cannot  be  clearly  identified with individual table rows; for example
       they cannot be used with aggregation.

              Caution: Avoid locking a row and  then  modifying  it  within  a
              later  savepoint  or  PL/pgSQL  exception  block.  A  subsequent
              rollback would cause the lock to be lost. For example:

              BEGIN;
              SELECT * FROM mytable WHERE key = 1 FOR UPDATE;
              SAVEPOINT s;
              UPDATE mytable SET ... WHERE key = 1;
              ROLLBACK TO s;

              After the ROLLBACK, the row is effectively unlocked, rather than
              returned  to  its  pre-savepoint  state  of being locked but not
              modified.  This hazard occurs if a row  locked  in  the  current
              transaction  is  updated  or  deleted,  or  if  a shared lock is
              upgraded to exclusive: in all these cases, the former lock state
              is  forgotten. If the transaction is then rolled back to a state
              between the original locking command and the subsequent  change,
              the  row  will  appear  not  to  be  locked  at  all. This is an
              implementation deficiency which will be addressed  in  a  future
              release of PostgreSQL.

              Caution:  It  is  possible for a SELECT command using both LIMIT
              and FOR UPDATE/SHARE clauses to return fewer rows than specified
              by  LIMIT.   This is because LIMIT is applied first. The command
              selects the specified number  of  rows,  but  might  then  block
              trying to obtain a lock on one or more of them.  Once the SELECT
              unblocks, the row might have been deleted or updated so that  it
              does  not  meet the query WHERE condition anymore, in which case
              it will not be returned.

              Caution: Similarly, it is possible for a  SELECT  command  using
              ORDER  BY and FOR UPDATE/SHARE to return rows out of order. This
              is because ORDER BY is applied first.  The  command  orders  the
              result,  but  might then block trying to obtain a lock on one or
              more of the rows. Once the SELECT unblocks, one of  the  ordered
              columns might have been modified and be returned out of order. A
              workaround is to perform SELECT ... FOR  UPDATE/SHARE  and  then
              SELECT ... ORDER BY.

   TABLE COMMAND
       The command

       TABLE name

       is completely equivalent to

       SELECT * FROM name

       It  can  be  used  as  a  top-level command or as a space-saving syntax
       variant in parts of complex queries.

EXAMPLES

       To join the table films with the table distributors:

       SELECT f.title, f.did, d.name, f.date_prod, f.kind
           FROM distributors d, films f
           WHERE f.did = d.did

              title       | did |     name     | date_prod  |   kind
       -------------------+-----+--------------+------------+----------
        The Third Man     | 101 | British Lion | 1949-12-23 | Drama
        The African Queen | 101 | British Lion | 1951-08-11 | Romantic
        ...

       To sum the column len of all films and group the results by kind:

       SELECT kind, sum(len) AS total FROM films GROUP BY kind;

          kind   | total
       ----------+-------
        Action   | 07:34
        Comedy   | 02:58
        Drama    | 14:28
        Musical  | 06:42
        Romantic | 04:38

       To sum the column len of all films, group the results by kind and  show
       those group totals that are less than 5 hours:

       SELECT kind, sum(len) AS total
           FROM films
           GROUP BY kind
           HAVING sum(len) < interval '5 hours';

          kind   | total
       ----------+-------
        Comedy   | 02:58
        Romantic | 04:38

       The following two examples are identical ways of sorting the individual
       results according to the contents of the second column (name):

       SELECT * FROM distributors ORDER BY name;
       SELECT * FROM distributors ORDER BY 2;

        did |       name
       -----+------------------
        109 | 20th Century Fox
        110 | Bavaria Atelier
        101 | British Lion
        107 | Columbia
        102 | Jean Luc Godard
        113 | Luso films
        104 | Mosfilm
        103 | Paramount
        106 | Toho
        105 | United Artists
        111 | Walt Disney
        112 | Warner Bros.
        108 | Westward

       The  next  example  shows  how  to  obtain  the  union  of  the  tables
       distributors  and  actors,  restricting the results to those that begin
       with the letter W in each table. Only distinct rows are wanted, so  the
       key word ALL is omitted.

       distributors:               actors:
        did |     name              id |     name
       -----+--------------        ----+----------------
        108 | Westward               1 | Woody Allen
        111 | Walt Disney            2 | Warren Beatty
        112 | Warner Bros.           3 | Walter Matthau
        ...                         ...

       SELECT distributors.name
           FROM distributors
           WHERE distributors.name LIKE 'W%'
       UNION
       SELECT actors.name
           FROM actors
           WHERE actors.name LIKE 'W%';

             name
       ----------------
        Walt Disney
        Walter Matthau
        Warner Bros.
        Warren Beatty
        Westward
        Woody Allen

       This  example shows how to use a function in the FROM clause, both with
       and without a column definition list:

       CREATE FUNCTION distributors(int) RETURNS SETOF distributors AS $$
           SELECT * FROM distributors WHERE did = $1;
       $$ LANGUAGE SQL;

       SELECT * FROM distributors(111);
        did |    name
       -----+-------------
        111 | Walt Disney

       CREATE FUNCTION distributors_2(int) RETURNS SETOF record AS $$
           SELECT * FROM distributors WHERE did = $1;
       $$ LANGUAGE SQL;

       SELECT * FROM distributors_2(111) AS (f1 int, f2 text);
        f1  |     f2
       -----+-------------
        111 | Walt Disney

       This example shows how to use a simple WITH clause:

       WITH t AS (
           SELECT random() as x FROM generate_series(1, 3)
         )
       SELECT * FROM t
       UNION ALL
       SELECT * FROM t

                x
       --------------------
         0.534150459803641
         0.520092216785997
        0.0735620250925422
         0.534150459803641
         0.520092216785997
        0.0735620250925422

       Notice that the WITH query was evaluated only once, so that we got  two
       sets of the same three random values.

       This  example  uses  WITH RECURSIVE to find all subordinates (direct or
       indirect) of the employee Mary, and their level of indirectness, from a
       table that shows only direct subordinates:

       WITH RECURSIVE employee_recursive(distance, employee_name, manager_name) AS (
           SELECT 1, employee_name, manager_name
           FROM employee
           WHERE manager_name = 'Mary'
         UNION ALL
           SELECT er.distance + 1, e.employee_name, e.manager_name
           FROM employee_recursive er, employee e
           WHERE er.employee_name = e.manager_name
         )
       SELECT distance, employee_name FROM employee_recursive;

       Notice  the  typical  form  of recursive queries: an initial condition,
       followed by UNION, followed by the recursive part of the query. Be sure
       that  the recursive part of the query will eventually return no tuples,
       or else the query will loop indefinitely. (See in the documentation for
       more examples.)

COMPATIBILITY

       Of  course,  the  SELECT statement is compatible with the SQL standard.
       But there are some extensions and some missing features.

   OMITTED FROM CLAUSES
       PostgreSQL allows one to omit the FROM clause. It has a straightforward
       use to compute the results of simple expressions:

       SELECT 2+2;

        ?column?
       ----------
               4

       Some  other  SQL databases cannot do this except by introducing a dummy
       one-row table from which to do the SELECT.

       Note that if a FROM clause is not specified, the query cannot reference
       any database tables. For example, the following query is invalid:

       SELECT distributors.* WHERE distributors.name = 'Westward';

       PostgreSQL releases prior to 8.1 would accept queries of this form, and
       add an implicit entry  to  the  query's  FROM  clause  for  each  table
       referenced  by  the  query.  This  is  no  longer the default behavior,
       because it does not comply with the SQL standard, and is considered  by
       many  to  be error-prone. For compatibility with applications that rely
       on this behavior the add_missing_from  configuration  variable  can  be
       enabled.

   OMITTING THE AS KEY WORD
       In  the SQL standard, the optional key word AS can be omitted before an
       output column name whenever the new column name is a valid column  name
       (that is, not the same as any reserved keyword). PostgreSQL is slightly
       more restrictive: AS is required if the new  column  name  matches  any
       keyword  at  all, reserved or not. Recommended practice is to use AS or
       double-quote output column names,  to  prevent  any  possible  conflict
       against future keyword additions.

       In  FROM items, both the standard and PostgreSQL allow AS to be omitted
       before an alias that is an unreserved keyword. But this is  impractical
       for output column names, because of syntactic ambiguities.

   ONLY AND PARENTHESES
       The SQL standard requires parentheses around the table name after ONLY,
       as in SELECT * FROM ONLY (tab1),  ONLY  (tab2)  WHERE  ....  PostgreSQL
       supports  that  as  well, but the parentheses are optional. (This point
       applies equally to all SQL commands supporting the ONLY option.)

   NAMESPACE AVAILABLE TO GROUP BY AND ORDER BY
       In the SQL-92 standard, an ORDER BY clause can only use  output  column
       names  or  numbers,  while  a  GROUP BY clause can only use expressions
       based on input column names. PostgreSQL extends each of  these  clauses
       to  allow  the  other  choice  as  well  (but  it  uses  the standard's
       interpretation if there is ambiguity).   PostgreSQL  also  allows  both
       clauses  to specify arbitrary expressions. Note that names appearing in
       an expression will always  be  taken  as  input-column  names,  not  as
       output-column names.

       SQL:1999  and  later  use  a slightly different definition which is not
       entirely upward  compatible  with  SQL-92.   In  most  cases,  however,
       PostgreSQL  will  interpret an ORDER BY or GROUP BY expression the same
       way SQL:1999 does.

   WINDOW CLAUSE RESTRICTIONS
       The  SQL  standard  provides  additional   options   for   the   window
       frame_clause.   PostgreSQL  currently  supports only the options listed
       above.

   LIMIT AND OFFSET
       The clauses LIMIT and OFFSET are PostgreSQL-specific syntax, also  used
       by  MySQL.  The SQL:2008 standard has introduced the clauses OFFSET ...
       FETCH {FIRST|NEXT} ... for the same functionality, as  shown  above  in
       LIMIT  Clause  [select(7)],  and  this  syntax is also used by IBM DB2.
       (Applications written for Oracle frequently use a workaround  involving
       the automatically generated rownum column, not available in PostgreSQL,
       to implement the effects of these clauses.)

   NONSTANDARD CLAUSES
       The clause DISTINCT ON is not defined in the SQL standard.