select

SELECT()                         SQL Commands                         SELECT()



NAME
       SELECT - Retrieves 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 ] [, ...] ]
           [ FOR UPDATE [ OF tablename [, ...] ] ]
           [ LIMIT { count | ALL } [ { OFFSET | , } start ]]

       where from_item can be:

       [ ONLY ] table_name [ * ]
           [ [ AS ] alias [ ( column_alias_list ) ] ]
       |
       ( select )
           [ AS ] alias [ ( column_alias_list ) ]
       |
       from_item [ NATURAL ] join_type from_item
           [ ON join_condition | USING ( join_column_list ) ]



   INPUTS
       expression
              The name of a table's column or an expression.

       output_name
              Specifies another name for an output column using the AS clause.
              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 the output_name cannot be used in the
              WHERE or HAVING clauses; write out the expression instead.

       from_item
              A table reference, sub-SELECT, or JOIN clause. See below for
              details.

       condition
              A boolean expression giving a result of true or false.  See the
              WHERE and HAVING clause descriptions below.

       select A select statement with all features except the ORDER BY, FOR
              UPDATE, and LIMIT clauses (even those can be used when the
              select is parenthesized).

       FROM items can contain:

       table_name
              The name 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 as of Postgres 7.1 this is the default
              behavior. (In releases before 7.1, ONLY was the default
              behavior.)

       alias  A substitute name for the preceding table_name.  An alias is
              used for brevity or to eliminate ambiguity for self-joins (where
              the same table is scanned multiple times). 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.

       join_type
              One of [ INNER ] JOIN, LEFT [ OUTER ] JOIN, RIGHT [ OUTER ]
              JOIN, FULL [ OUTER ] JOIN, or CROSS JOIN.  For INNER and OUTER
              join types, exactly one of NATURAL, ON join_condition, or USING
              ( join_column_list ) must appear. For CROSS JOIN, none of these
              items may appear.

       join_condition
              A qualification condition. This is similar to the WHERE
              condition except that it only applies to the two from_items
              being joined in this JOIN clause.

       join_column_list
              A USING column list ( a, b, ... ) is shorthand for the ON
              condition left_table.a = right_table.a AND left_table.b =
              right_table.b ...

   OUTPUTS
       Rows   The complete set of rows resulting from the query specification.

       count  The count of rows returned by the query.

DESCRIPTION
       SELECT will return rows from one or more tables.  Candidates for
       selection are rows which satisfy the WHERE condition; if WHERE is
       omitted, all rows are candidates.  (See WHERE Clause [select(l)].)

       Actually, the returned rows are not directly the rows produced by the
       FROM/WHERE/GROUP BY/HAVING clauses; rather, the output rows are formed
       by computing the SELECT output expressions for each selected row.  *
       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.

       DISTINCT will eliminate duplicate rows from the result.  ALL (the
       default) will return all candidate rows, including duplicates.

       DISTINCT ON eliminates rows that match on all the specified
       expressions, keeping only the first row of each set of duplicates. The
       DISTINCT ON expressions are interpreted using the same rules as for
       ORDER BY items; see below.  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 weatherReports
               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 of unpredictable age for each
       location.

       The GROUP BY clause allows a user to divide a table into groups of rows
       that match on one or more values.  (See GROUP BY Clause [select(l)].)

       The HAVING clause allows selection of only those groups of rows meeting
       the specified condition.  (See HAVING Clause [select(l)].)

       The ORDER BY clause causes the returned rows to be sorted in a
       specified order. If ORDER BY is not given, the rows are returned in
       whatever order the system finds cheapest to produce.  (See ORDER BY
       Clause [select(l)].)

       SELECT queries can be combined using UNION, INTERSECT, and EXCEPT
       operators. Use parentheses if necessary to determine the ordering of
       these operators.

       The UNION operator computes the collection of rows returned by the
       queries involved.  Duplicate rows are eliminated unless ALL is
       specified.  (See UNION Clause [select(l)].)

       The INTERSECT operator computes the rows that are common to both
       queries.  Duplicate rows are eliminated unless ALL is specified.  (See
       INTERSECT Clause [select(l)].)

       The EXCEPT operator computes the rows returned by the first query but
       not the second query.  Duplicate rows are eliminated unless ALL is
       specified.  (See EXCEPT Clause [select(l)].)

       The FOR UPDATE clause allows the SELECT statement to perform exclusive
       locking of selected rows.

       The LIMIT clause allows a subset of the rows produced by the query to
       be returned to the user.  (See LIMIT Clause [select(l)].)

       You must have SELECT privilege to a table to read its values (See the
       GRANT/REVOKE statements).

   FROM CLAUSE
       The FROM clause specifies one or more source tables for the SELECT.  If
       multiple sources are specified, the result is conceptually the
       Cartesian product of all the rows in all the sources --- but usually
       qualification conditions are added to restrict the returned rows to a
       small subset of the Cartesian product.

       When a FROM item is a simple table name, it implicitly includes rows
       from sub-tables (inheritance children) of the table.  ONLY will
       suppress rows from sub-tables of the table. Before Postgres 7.1, this
       was the default result, and adding sub-tables was done by appending *
       to the table name.  This old behaviour is available via the command SET
       SQL_Inheritance TO OFF;

       A FROM item can also be a parenthesized sub-SELECT (note that an alias
       clause is required for a sub-SELECT!). This is an extremely handy
       feature since it's the only way to get multiple levels of grouping,
       aggregation, or sorting in a single query.

       Finally, a FROM item can be a JOIN clause, which combines two simpler
       FROM items. (Use parentheses if necessary to determine the order of
       nesting.)

       A CROSS JOIN or INNER JOIN is 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 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 ON condition), plus one copy of
       each row in the left-hand table for which there was no right-hand row
       that passed the ON condition. This left-hand row is extended to the
       full width of the joined table by inserting NULLs for the right-hand
       columns.  Note that only the JOIN's own ON or USING condition is
       considered while deciding which rows have matches. Outer ON or WHERE
       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).

       For all the JOIN types except CROSS JOIN, you must write exactly one of
       ON join_condition, USING ( join_column_list ), or NATURAL. ON is the
       most general case: you can write any qualification expression involving
       the two tables to be joined.  A USING column list ( a, b, ... ) is
       shorthand for the ON condition 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 is shorthand for a USING list that mentions all
       similarly-named columns in the tables.

   WHERE CLAUSE
       The optional WHERE condition has the general form:

       WHERE boolean_expr


       boolean_expr can consist of any expression which evaluates to a boolean
       value.  In many cases, this expression will be:

            expr cond_op expr


       or

            log_op expr


       where cond_op can be one of: =, <, <=, >, >= or <>, a conditional
       operator like ALL, ANY, IN, LIKE, or a locally defined operator, and
       log_op can be one of: AND, OR, NOT.  SELECT will ignore all rows for
       which the WHERE condition does not return TRUE.

   GROUP BY CLAUSE
       GROUP BY specifies a grouped table derived by the application of this
       clause:

       GROUP BY expression [, ...]



       GROUP BY will condense into a single row all selected rows that share
       the same values for the grouped columns. Aggregate functions, if any,
       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 output expression(s) to refer
       to ungrouped columns except within aggregate functions, since there
       would be more than one possible value to return for an ungrouped
       column.

       A GROUP BY item can be an input column name, or the name or ordinal
       number of an output column (SELECT expression), 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.

   HAVING CLAUSE
       The optional HAVING condition has the general form:

       HAVING boolean_expr


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

       HAVING specifies a grouped table derived by the elimination of group
       rows that do not satisfy the boolean_expr.  HAVING is different from
       WHERE: WHERE filters individual rows before application of GROUP BY,
       while HAVING filters group rows created by GROUP BY.

       Each column referenced in boolean_expr shall unambiguously reference a
       grouping column, unless the reference appears within an aggregate
       function.

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



       An ORDER BY item can be the name or ordinal number of an output column
       (SELECT expression), or it can be an arbitrary expression formed from
       input-column values. In case of ambiguity, an ORDER BY name will be
       interpreted as an output-column name.

       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 proper name.  This is
       never absolutely necessary because it is always possible to assign a
       name to a result column using the AS clause, e.g.:

       SELECT title, date_prod + 1 AS newlen FROM films ORDER BY newlen;



       It is also possible to ORDER BY arbitrary expressions (an extension to
       SQL92), including fields that do not appear in the SELECT result list.
       Thus the following statement is legal:

       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 query may only specify an
       output column name or number, not an expression.

       Note that if an ORDER BY item 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
       mandated by the SQL92 standard.

       Optionally one may add the keyword DESC (descending) or ASC (ascending)
       after each column name in the ORDER BY clause.  If not specified, ASC
       is assumed by default. Alternatively, a specific ordering operator name
       may be specified. ASC is equivalent to USING < and DESC is equivalent
       to USING >.

   UNION CLAUSE
       table_query UNION [ ALL ] table_query
           [ ORDER BY expression [ ASC | DESC | USING operator ] [, ...] ]
           [ LIMIT { count | ALL } [ { OFFSET | , } start ]]


       where table_query specifies any select expression without an ORDER BY,
       FOR UPDATE, or LIMIT clause. (ORDER BY and LIMIT can be attached to a
       sub-expression 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 collection (set union) of the rows
       returned by the queries involved.  The two SELECTs 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.

       Multiple UNION operators in 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 a UNION.

   INTERSECT CLAUSE
       table_query INTERSECT [ ALL ] table_query
           [ ORDER BY expression [ ASC | DESC | USING operator ] [, ...] ]
           [ LIMIT { count | ALL } [ { OFFSET | , } start ]]


       where table_query specifies any select expression without an ORDER BY,
       FOR UPDATE, or LIMIT clause.

       INTERSECT is similar to UNION, except that it produces only rows that
       appear in both query outputs, rather than rows that appear in either.

       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 L and
       n duplicates in R will appear min(m,n) times.

       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) unless otherwise specified by parentheses.

   EXCEPT CLAUSE
       table_query EXCEPT [ ALL ] table_query
           [ ORDER BY expression [ ASC | DESC | USING operator ] [, ...] ]
           [ LIMIT { count | ALL } [ { OFFSET | , } start ]]


       where table_query specifies any select expression without an ORDER BY,
       FOR UPDATE, or LIMIT clause.

       EXCEPT is similar to UNION, except that it produces only rows that
       appear in the left query's output but not in the right query's output.

       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 L and n
       duplicates in R will appear max(m-n,0) times.

       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.

   LIMIT CLAUSE
           LIMIT { count | ALL } [ { OFFSET | , } start ]
           OFFSET start


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

       LIMIT allows you to retrieve just a portion of the rows that are
       generated by the rest of the query. If a limit count is given, no more
       than that many rows will be returned. If an offset is given, that many
       rows will be skipped before starting to return rows.

       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 may be asking for the
       tenth through twentieth rows, but tenth through twentieth in what
       ordering? You don't know what ordering, unless you specified ORDER BY.

       As of Postgres 7.0, the query optimizer 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 give 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.

USAGE
       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
        Une Femme est une Femme   | 102 | Jean Luc Godard  | 1961-03-12 | Romantic
        Vertigo                   | 103 | Paramount        | 1958-11-14 | Action
        Becket                    | 103 | Paramount        | 1964-02-03 | Drama
        48 Hrs                    | 103 | Paramount        | 1982-10-22 | Action
        War and Peace             | 104 | Mosfilm          | 1967-02-12 | Drama
        West Side Story           | 105 | United Artists   | 1961-01-03 | Musical
        Bananas                   | 105 | United Artists   | 1971-07-13 | Comedy
        Yojimbo                   | 106 | Toho             | 1961-06-16 | Drama
        There's a Girl in my Soup | 107 | Columbia         | 1970-06-11 | Comedy
        Taxi Driver               | 107 | Columbia         | 1975-05-15 | Action
        Absence of Malice         | 107 | Columbia         | 1981-11-15 | Action
        Storia di una donna       | 108 | Westward         | 1970-08-15 | Romantic
        The King and I            | 109 | 20th Century Fox | 1956-08-11 | Musical
        Das Boot                  | 110 | Bavaria Atelier  | 1981-11-11 | Drama
        Bed Knobs and Broomsticks | 111 | Walt Disney      |            | Musical
       (17 rows)


       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
       (5 rows)


       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 hour';

        kind     | total
       ----------+-------
        Comedy   | 02:58
        Romantic | 04:38
       (2 rows)


       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
       (13 rows)


       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 each table. Only distinct rows are wanted, so the ALL keyword 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


COMPATIBILITY
   EXTENSIONS
       Postgres allows one to omit the FROM clause from a query. This feature
       was retained from the original PostQuel query language. It has a
       straightforward use to compute the results of simple constant
       expressions:

       SELECT 2+2;

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


       Some other DBMSes cannot do this except by introducing a dummy one-row
       table to do the select from. A less obvious use is to abbreviate a
       normal select from one or more tables:

       SELECT distributors.* WHERE name = 'Westward';

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


       This works because an implicit FROM item is added for each table that
       is referenced in the query but not mentioned in FROM. While this is a
       convenient shorthand, it's easy to misuse. For example, the query

       SELECT distributors.* FROM distributors d;


       is probably a mistake; most likely the user meant

       SELECT d.* FROM distributors d;


       rather than the unconstrained join

       SELECT distributors.* FROM distributors d, distributors distributors;


       that he will actually get. To help detect this sort of mistake,
       Postgres 7.1 and later will warn if the implicit-FROM feature is used
       in a query that also contains an explicit FROM clause.

   SQL92
   SELECT CLAUSE
       In the SQL92 standard, the optional keyword "AS" is just noise and can
       be omitted without affecting the meaning.  The Postgres parser requires
       this keyword when renaming output columns because the type
       extensibility features lead to parsing ambiguities in this context.
       "AS" is optional in FROM items, however.

       The DISTINCT ON phrase is not part of SQL92.  Nor are LIMIT and OFFSET.

       In SQL92, an ORDER BY clause may only use result column names or
       numbers, while a GROUP BY clause may only use input column names.
       Postgres extends each of these clauses to allow the other choice as
       well (but it uses the standard's interpretation if there is ambiguity).
       Postgres 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.

   UNION/INTERSECT/EXCEPT CLAUSE
       The SQL92 syntax for UNION/INTERSECT/EXCEPT allows an additional
       CORRESPONDING BY option:


       table_query UNION [ALL]
           [CORRESPONDING [BY (column [,...])]]
           table_query



       The CORRESPONDING BY clause is not supported by Postgres.



SQL - Language Statements        29 March 2001                        SELECT()