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SELECT()			 SQL Commands			      SELECT()

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 ele‐
	      ment 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	dupli‐
	      cates. (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 Carte‐
       sian 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 indi‐
	      cate that descendant tables are to be scanned, but in  the  cur‐
	      rent  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 remain‐
	      der 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	 espe‐
	      cially  useful  for  functions  that return result sets, but any
	      function can be used.) This acts as though its output were  cre‐
	      ated 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 ( col‐
	      umn_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  equiva‐
       lent  to INNER JOIN ON (TRUE), that is, no rows are removed by qualifi‐
       cation.	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  equiva‐
	      lent 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 elimi‐
       nated 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 mak‐
       ing  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 refer‐
       ence a grouping column, unless the reference appears within  an	aggre‐
       gate 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  ta‐
       ble.

   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 parenthe‐
       ses, 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 com‐
       patible data types.

       The result of UNION does not contain any duplicate rows unless the  ALL
       option  is  specified.  ALL prevents elimination of duplicates. (There‐
       fore, 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 intersec‐
       tion 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 out‐
       put 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  com‐
       patible with the SQL standard.

       Optionally  one	can add the key word ASC (ascending) or DESC (descend‐
       ing) 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  val‐
       ues.  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 colla‐
       tion order that was established when the database cluster was  initial‐
       ized.

   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	speci‐
       fies 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 expres‐
       sion(s). The ORDER BY clause will normally contain  additional  expres‐
       sion(s)	that determine the desired precedence of rows within each DIS‐
       TINCT 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 spec‐
       ifies  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 con‐
       strains 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 with‐
       out 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 nec‐
       essary 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 roll‐
	      back 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 mod‐
	      ified.  This hazard occurs if a row locked in the current trans‐
	      action is updated or deleted, or if a shared lock is upgraded to
	      exclusive: in all these cases, the former lock state is  forgot‐
	      ten.  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	 Post‐
	      greSQL.

	      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  try‐
	      ing  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.

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  distribu‐
       tors  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 refer‐
       enced 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 extensibil‐
       ity 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 interpre‐
       tation  if there is ambiguity).	PostgreSQL also allows both clauses to
       specify arbitrary expressions. Note that names appearing in an  expres‐
       sion  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, Post‐
       greSQL 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.

SQL - Language Statements	  2008-02-01			      SELECT()
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