Seth Woolley's Man Viewer

Manual for select - man 7 select

([section] manual, -k keyword, -K [section] search, -f whatis)
man plain no title

SELECT(7)                        SQL Commands                        SELECT(7)



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(2,7,2 select_tut) ]
           [ ORDER BY expression [ ASC | DESC | USING operator ] [, ...] ]
           [ LIMIT { count | ALL } ]
           [ OFFSET start ]
           [ FOR UPDATE [ OF table_name [, ...] ] ]

       where from_item can be one of:

           [ ONLY ] table_name [ * ] [ [ AS ] alias [ ( column_alias [, ...] ) ] ]
           ( select(2,7,2 select_tut) ) [ 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 [, ...] ) ]

       [Comment:  FIXME:  This last syntax is incorrect if(3,n) the join(1,n) type is an
       INNER or OUTER join(1,n) (in(1,8) which case one of NATURAL, ON ..., or USING ...
       is mandatory, not optional). What's the best way to fix this?]

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

       1.     All elements in(1,8) the FROM list are computed.   (Each  element  in(1,8)
              the FROM list is a real or virtual(5,8) table.) If more than one ele-
              ment is specified  in(1,8)  the  FROM  list,  they  are  cross-joined
              together.  (See FROM Clause [select(2,7,2 select_tut)(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(2,7,2 select_tut)(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(2,7,2 select_tut)(7)]  and  HAVING
              Clause [select(2,7,2 select_tut)(7)] below.)

       4.     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(1,8) one
              or both of the result sets. The INTERSECT operator  returns  all
              rows  that are strictly in(1,8) both result sets. The EXCEPT operator
              returns the rows that are in(1,8) the first result set(7,n,1 builtins) but not in(1,8) the
              second. In all three cases, duplicate rows are eliminated unless
              ALL is  specified.  (See  UNION  Clause  [select(2,7,2 select_tut)(7)],  INTERSECT
              Clause [select(2,7,2 select_tut)(l)], and EXCEPT Clause [select(2,7,2 select_tut)(7)] below.)

       5.     The  actual  output  rows are computed the SELECT output expres-
              sions for  each  selected  row.  (See  SELECT  List  [select(2,7,2 select_tut)(7)]
              below.)

       6.     If  the  ORDER  BY  clause  is  specified, the returned rows are
              sorted in(1,8) the specified order. If ORDER BY  is  not  given,  the
              rows  are returned in(1,8) whatever order the system finds fastest to
              produce. (See ORDER BY Clause [select(2,7,2 select_tut)(7)] below.)

       7.     If the LIMIT or OFFSET clause is specified, the SELECT statement
              only  returns  a  subset  of  the result rows. (See LIMIT Clause
              [select(2,7,2 select_tut)(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  dupli-
              cates. (See DISTINCT Clause [select(2,7,2 select_tut)(7)] below.)

       9.     The  FOR  UPDATE  clause causes the SELECT statement to lock the
              selected rows against concurrent updates. (See FOR UPDATE Clause
              [select(2,7,2 select_tut)(7)] below.)


       You  must  have SELECT privilege on a table to read(2,n,1 builtins) its values. The use
       of FOR UPDATE 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(1,n)) of all the sources. But usually  qualification  conditions
       are added to restrict the returned rows to a small subset of the Carte-
       sian product.

       FROM-clause elements can contain:

       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(3,n)
              any)  are  scanned. * can be appended to the table name to indi-
              cate that descendant tables are to be scanned, but in(1,8)  the  cur-
              rent  version(1,3,5), 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_interitance 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(2,7,2 select_tut) A sub-SELECT can appear in(1,8) 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.

       function_name
              Function calls can appear in(1,8) 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 may 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(1,8) 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(1,n) types, a join(1,n) 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 may appear.

       A  JOIN  clause, combines two FROM items. (Use parentheses if(3,n) necessary
       to determine the order of nesting.)

       CROSS JOIN and INNER JOIN produce a simple Cartesian product, the  same
       as  you get from listing the two items at the top level of FROM.  CROSS
       JOIN is equivalent to INNER JOIN  ON  (true),  that  is,  no  rows  are
       removed  by qualification.  These join(1,n) types are just a notational con-
       venience, since they do nothing you couldn't do  with  plain  FROM  and
       WHERE.

       LEFT  OUTER  JOIN  returns  all rows in(1,8) the qualified Cartesian product
       (i.e., all combined rows that pass its join(1,n) condition), plus  one  copy
       of  each  row  in(1,8) the left-hand table for which there was no right-hand
       row that passed the join(1,n) 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 clauses  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(1,8)  a  value  of  type
              boolean (similar to a WHERE clause) that specifies which rows in(1,8)
              a join(1,n) 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(1,8) the join(1,n) output, not both.

       NATURAL
              NATURAL  is shorthand for a USING list that mentions all columns
              in(1,8) 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(3,n) 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),  or  it  can be 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(3,n) 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(1,8) condition must unambiguously refer-
       ence  a  grouping column, unless the reference appears within an aggre-
       gate function.

   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, or
       FOR UPDATE clause.  (ORDER BY and LIMIT can be attached to a subexpres-
       sion if(3,n) it is  enclosed  in(1,8)  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(7,n,1 builtins) union of the rows returned  by  the
       involved  SELECT  statements.  A  row is in(1,8) the set(7,n,1 builtins) union of two result
       sets if(3,n) it appears in(1,8) 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.

       Multiple UNION operators in(1,8) the same  SELECT  statement  are  evaluated
       left to right, unless otherwise indicated by parentheses.

       Currently, FOR UPDATE may not be specified either for a UNION result or
       for the inputs of 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, or
       FOR UPDATE clause.

       The  INTERSECT  operator  computes  the  set(7,n,1 builtins)  intersection  of the rows
       returned by the involved SELECT statements. A row is in(1,8)  the  intersec-
       tion of two result sets if(3,n) it appears in(1,8) 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(1,8)  the
       left  table  and  n  duplicates in(1,8) the right table will appear min(m,n)
       times in(1,8) the result set.

       Multiple INTERSECT operators in(1,8) 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(2,n,1 builtins) as
       A UNION (B INTERSECT C).

   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, or
       FOR UPDATE clause.

       The EXCEPT operator computes the set(7,n,1 builtins) of rows that are in(1,8) the result  of
       the left SELECT statement but not in(1,8) 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(1,8) the left
       table  and n duplicates in(1,8) the right table will appear max(m-n,0) times
       in(1,8) the result set.

       Multiple EXCEPT operators in(1,8) the same SELECT  statement  are  evaluated
       left  to  right,  unless parentheses dictate otherwise. EXCEPT binds at
       the same level as UNION.

   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(1,8) 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(1,8)
       ORDER BY and GROUP BY clauses, but not in(1,8) the WHERE or HAVING  clauses;
       there you must write(1,2) out the expression instead.

       Instead  of  an  expression,  *  can be written in(1,8) the output list as a
       shorthand for all the columns of the selected rows. Also, one can write(1,2)
       table_name.*  as  a shorthand for the columns coming from just that ta-
       ble.

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

       ORDER BY expression [ ASC | DESC | USING operator ] [, ...]

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

       The ORDER BY clause causes the result rows to be  sorted  according  to
       the specified expressions. If two rows are equal according to the left-
       most expression, the are compared according to the next expression  and
       so  on.  If they are equal according to all specified expressions, they
       are returned in(1,8) random(3,4,6) order.

       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(1,8)  the  ORDER  BY
       clause, including columns that do not appear in(1,8) 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 may 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(1,8) the same situation. This inconsistency is made to be com-
       patible with the SQL standard.

       Optionally one may add the key word ASC (ascending) or  DESC  (descend-
       ing)  after  each  expression in(1,8) the ORDER BY clause. If not specified,
       ASC is assumed by default. Alternatively, a specific ordering  operator
       name  may  be specified in(1,8) the USING clause.  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(1,3)
       ordering is, and it might correspond to operators with other names.)

       The null value sorts higher than any other value. In other words,  with
       ascending  sort(1,3) order, null values sort(1,3) at the end, and with descending
       sort(1,3) order, null values sort(1,3) at the beginning.

       Character-string data is sorted according to the locale-specific colla-
       tion  order that was established when the database cluster was initial-
       ized.

   LIMIT CLAUSE
       The LIMIT clause consists of two independent clauses:

       LIMIT { count | ALL }
       OFFSET start

       count specifies the maximum number of rows to return, and start  speci-
       fies the number of rows to skip before starting to return rows.

       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 may be asking for the
       tenth through twentieth rows,  but  tenth  through  twentieth  in(1,8)  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(2,7,2 select_tut) 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(1,8) any particular order unless ORDER BY is  used  to
       constrain the order.

   DISTINCT CLAUSE
       If  DISTINCT  is  specified,  all  duplicate  rows are removed from the
       result set(7,n,1 builtins) (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(7,n,1 builtins)
       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(7,n,1 builtins) is unpredictable unless
       ORDER  BY  is  used  to  ensure that the desired row appears first. For
       example,

       SELECT DISTINCT ON (location) location, time(1,2,n), report
           FROM weather_reports
           ORDER BY location, time(1,2,n) DESC;

       retrieves the most recent weather report for each location. But  if(3,n)  we
       had not used ORDER BY to force descending order of time(1,2,n) values for each
       location, we'd have gotten a report from an unpredictable time(1,2,n) for each
       location.

   FOR UPDATE CLAUSE
       The FOR UPDATE clause has this form:

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


       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(3,n) 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(3,n) the row was deleted).
       For further discussion see the chapter called  ``Concurrency  Control''
       in(1,8) the documentation.

       If  specific tables are named(5,8) in(1,8) FOR UPDATE, then only rows coming from
       those tables are locked; any other tables used in(1,8) the SELECT are simply
       read(2,n,1 builtins) as usual.

       FOR  UPDATE  cannot  be  used  in(1,8) contexts where returned rows can't be
       clearly identified with individual table rows; for example it can't  be
       used with aggregation.

       FOR  UPDATE  may  appear before LIMIT for compatibility with PostgreSQL
       versions before 7.3. It effectively executes after LIMIT, however,  and
       so that is the recommended place to write(1,2) it.

EXAMPLES
       To join(1,n) 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(1,3) 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


       This  example  shows how to obtain the union of the tables distributors
       and actors, restricting the results to those that begin with  letter  W
       in(1,8)  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(1,8) 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;

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

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

       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.

       A less(1,3) obvious use is to abbreviate a normal SELECT from tables:

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

        did |   name
       -----+----------
        108 | Westward

       This works because an implicit FROM item is added for each  table  that
       is  referenced in(1,8) other parts of the SELECT statement but not mentioned
       in(1,8) FROM.

       While this is a convenient shorthand, it's easy to misuse. For example,
       the command

       SELECT distributors.* FROM distributors d;

       is probably a mistake; most likely the user meant

       SELECT d.* FROM distributors d;

       rather than the unconstrained join(1,n)

       SELECT distributors.* FROM distributors d, distributors distributors;

       that  he  will actually get. To help detect this sort(1,3) of mistake, Post-
       greSQL will warn if(3,n) the implicit-FROM  feature  is  used  in(1,8)  a  SELECT
       statement  that also contains an explicit FROM clause. Also, it is pos-
       sible to disable the implicit-FROM feature  by  setting  the  ADD_MISS-
       ING_FROM parameter to false.

   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(1,8)
       FROM items, however.

   NAMESPACE AVAILABLE TO GROUP BY AND ORDER BY
       In  the  SQL92  standard, an ORDER BY clause may only use result column
       names or numbers, while a GROUP BY  clause  may  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(3,n) there is ambiguity).  PostgreSQL also allows both clauses to
       specify arbitrary expressions. Note that names appearing in(1,8) an  expres-
       sion  will  always be taken as input-column names, not as result-column
       names.

       SQL99 uses a slightly different definition which is not upward compati-
       ble  with  SQL92.  In most cases, however, PostgreSQL will interpret an
       ORDER BY or GROUP BY expression the same way SQL99 does.

   NONSTANDARD CLAUSES
       The clauses DISTINCT ON, LIMIT, and OFFSET are not defined in(1,8)  the  SQL
       standard.



SQL - Language Statements         2003-11-02                         SELECT(7)

References for this manual (incoming links)