Provided by: postgresql-client-8.3_8.3.8-1_i386 bug

NAME

       SELECT - retrieve rows from a table or view

SYNOPSIS

       SELECT [ ALL | DISTINCT [ ON ( expression [, ...] ) ] ]
           * | expression [ AS output_name ] [, ...]
           [ FROM from_item [, ...] ]
           [ WHERE condition ]
           [ GROUP BY expression [, ...] ]
           [ HAVING condition [, ...] ]
           [ { UNION | INTERSECT | EXCEPT } [ ALL ] select ]
           [ ORDER BY expression [ ASC | DESC | USING operator ] [ NULLS { FIRST | LAST } ] [, ...] ]
           [ LIMIT { count | ALL } ]
           [ OFFSET start ]
           [ 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 [, ...] ) ]
           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 [, ...] ) ]

DESCRIPTION

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

       1.     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.)

       2.     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.)

       3.     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.)

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

       5.     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(l)], and EXCEPT Clause [select(7)] below.)

       6.     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.)

       7.     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.)

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

       9.     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 a table to read its values. The use
       of FOR UPDATE or FOR SHARE requires UPDATE privilege as well.

PARAMETERS

   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 all its  descendant  tables  (if
              any)  are  scanned.  *  can  be  appended  to  the table name to
              indicate that descendant tables are to be scanned,  but  in  the
              current  version,  this  is  the  default behavior. (In releases
              before 7.1, ONLY was the default behavior.) The default behavior
              can  be  modified  by changing the sql_inheritance configuration
              option.

       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.

       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

              · [ INNER ] JOIN

              · LEFT [ OUTER ] JOIN

              · RIGHT [ OUTER ] JOIN

              · FULL [ OUTER ] JOIN

              · 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.

   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. Using the clause AS output_name, another name can be  specified
       for  an  output column. This name is primarily used to label the column
       for display. It can also 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, one can write
       table_name.* as a shorthand for  the  columns  coming  from  just  that
       table.

   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 result 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 a result 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 result 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 a result
       column name and an input column name, ORDER BY will interpret it as the
       result  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 cluster was
       initialized.

   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.

       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.

       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 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.

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

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.

   THE AS KEY WORD
       In the SQL standard, the optional key word AS is just noise and can  be
       omitted  without  affecting the meaning. The PostgreSQL parser requires
       this  key  word  when  renaming  output  columns   because   the   type
       extensibility  features  lead to parsing ambiguities without it.  AS is
       optional in FROM items, however.

   NAMESPACE AVAILABLE TO GROUP BY AND ORDER BY
       In the SQL-92 standard, an ORDER BY clause can only use  result  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
       result-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.

   NONSTANDARD CLAUSES
       The clauses DISTINCT ON, LIMIT, and OFFSET are not defined in  the  SQL
       standard.