<refentry id="SQL-SELECT">
 <refmeta>
  <refentrytitle>
   SELECT
  </refentrytitle>
  <refmiscinfo>SQL - Language Statements</refmiscinfo>
 </refmeta>
 <refnamediv>
  <refname>
   SELECT
  </refname>
  <refpurpose>
   Retrieve rows from a table or view.
  </refpurpose></refnamediv>
 <refsynopsisdiv>
  <refsynopsisdivinfo>
   <date>1998-09-06</date>
  </refsynopsisdivinfo>
  <synopsis>
SELECT [ALL|DISTINCT]
    <replaceable class="PARAMETER">expression</replaceable> [AS <replaceable class="PARAMETER">name</replaceable>] [, ...]
    [INTO [TABLE] <replaceable class="PARAMETER">intable</replaceable>]
    [FROM <replaceable class="PARAMETER">table</replaceable> [<replaceable class="PARAMETER">alias</replaceable>] [, ...] ]
    [WHERE <replaceable class="PARAMETER">condition</replaceable>]
    [GROUP BY <replaceable class="PARAMETER">column</replaceable> [, ...] ]
    [HAVING <replaceable class="PARAMETER">condition</replaceable> [, ...] ]
    [UNION [ALL] <replaceable class="PARAMETER">select</replaceable>]
    [ORDER BY <replaceable class="PARAMETER">column</replaceable> [ASC | DESC] [, ...] ]
  </synopsis>
  
  <refsect2 id="R2-SQL-SELECT-1">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    Inputs
   </title>
   
   <para>
    <variablelist>
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">expression</replaceable>
      </term>
      <listitem>
       <para>
	The name of a table's column or an expression.
       </para>
      </listitem>
     </varlistentry>
     
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">name</replaceable>
      </term>
      <listitem>
       <para>
	Specifies another name for a column or an expression using
	the AS clause. <replaceable class="PARAMETER">name</replaceable>
	cannot be used in the WHERE
	condition. It can, however, be referenced in associated
	ORDER BY or GROUP BY clauses.
       </para>
      </listitem>
     </varlistentry>
     
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">intable</replaceable>
      </term>
      <listitem>
       <para>
	If the INTO TABLE clause is specified, the result of the
	query will be stored in another table with the indicated
	name.
	If <replaceable class="PARAMETER">intable</replaceable> does
	not exist, it will be created automatically.
	
	<note>
	 <para>
	  The <command>CREATE TABLE AS</command> statement will also
	  create a new  table from a select query.
	 </para>
	</note>
       </para>
      </listitem>
     </varlistentry>
     
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">table</replaceable>
      </term>
      <listitem>
       <para>
	The name of an existing table referenced by the FROM clause.
       </para>
      </listitem>
     </varlistentry>
     
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">alias</replaceable>
      </term>
      <listitem>
       <para>
	An alternate name for the preceding
	<replaceable class="PARAMETER">table</replaceable>.
	It is used for brevity or to eliminate ambiguity for joins
	within a single table.
       </para>
      </listitem>
     </varlistentry>
     
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">condition</replaceable>
      </term>
      <listitem>
       <para>
	A boolean expression giving a result of true or false.
	See the WHERE clause.
       </para>
      </listitem>
     </varlistentry>
     
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">column</replaceable>
      </term>
      <listitem>
       <para>
	The name of a table's column.
       </para>
      </listitem>
     </varlistentry>
     
     <varlistentry>
      <term>
       <replaceable class="PARAMETER">select</replaceable>
      </term>
      <listitem>
       <para>
	A select statement with all features except the ORDER BY clause.
       </para>
      </listitem>
     </varlistentry>
     
    </variablelist>
   </para>
  </refsect2>
  
  <refsect2 id="R2-SQL-SELECT-2">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    Outputs
   </title>
   <variablelist>
    <varlistentry>
     <term>
      Rows
     </term>
     <listitem>
      <para>
       The complete set of rows resulting from the query specification.
      </para>
     </listitem>
    </varlistentry>
    
    <varlistentry>
     <term>
      <returnvalue>count</returnvalue>
     </term>
     <listitem>
      <para>
       The count of rows returned by the query.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
   
  </refsect2>
 </refsynopsisdiv>
 
 <refsect1 id="R1-SQL-SELECT-1">
  <refsect1info>
   <date>1998-09-06</date>
  </refsect1info>
  <title>
   Description
  </title>
  <para>
   SELECT will get all rows which satisfy the WHERE condition
   or all rows of a table if WHERE is omitted.</para>
   
  <para>
   The GROUP BY clause allows a user to divide a table
   conceptually into groups. (See GROUP BY clause).</para>
   
  <para>
   The HAVING clause specifies a grouped table derived by the
   elimination of groups from the result of the previously
   specified clause. (See HAVING clause).</para>
   
  <para>
   The ORDER BY clause allows a user to specify that he/she
   wishes the rows sorted according to the ASCending or 
   DESCending mode operator. (See ORDER BY clause)</para>
   
  <para>
   The UNION clause specifies a table derived from a Cartesian
   product union join. (See UNION clause).</para>
   
  <para>
   You must have SELECT privilege to a table to read its values
   (See GRANT/REVOKE statements).</para>
   
  <refsect2 id="R2-SQL-WHERE-2">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    WHERE clause
   </title>
   <para>
    The optional WHERE condition has the general form:
    
    <synopsis>
WHERE <replaceable class="PARAMETER">expr</replaceable> <replaceable class="PARAMETER">cond_op</replaceable> <replaceable class="PARAMETER">expr</replaceable> [<replaceable class="PARAMETER">log_op</replaceable> ...]
    </synopsis>
    
    where <replaceable class="PARAMETER">cond_op</replaceable> can be
    one of: =, &lt;, &lt;=, &gt;, &gt;=, &lt;&gt;
    or a conditional operator like ALL, ANY, IN, LIKE, et cetera
    and <replaceable class="PARAMETER">log_op</replaceable> can be one 
    of: AND, OR, NOT.
    The comparison returns either TRUE or FALSE and all
    instances will be discarded
    if the expression evaluates to FALSE.
   </para>
  </refsect2>
  
  <refsect2 id="R2-SQL-GROUPBY-2">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    GROUP BY clause
   </title>
   <para>
    GROUP BY specifies a grouped table derived by the application
    of the this clause:
    <synopsis>
     GROUP BY <replaceable class="PARAMETER">column</replaceable> [, ...]
    </synopsis></para></refsect2>
    
  <refsect2 id="R2-SQL-HAVING-2">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    HAVING clause
   </title>
   <para>
    The optional HAVING condition has the general form:
    
    <synopsis>
HAVING <replaceable class="PARAMETER">cond_expr</replaceable>
    </synopsis>
    
    where <replaceable class="PARAMETER">cond_expr</replaceable> is the same
    as specified for the WHERE clause.</para>
    
   <para>
    HAVING specifies a grouped table derived by the elimination
    of groups from the result of the previously specified clause
    that do not meet the <replaceable class="PARAMETER">cond_expr</replaceable>.</para>
    
   <para>
    Each column referenced in <replaceable class="PARAMETER">cond_expr</replaceable> shall unambiguously
    reference a grouping column.
   </para>
  </refsect2>
  
  <refsect2 id="R2-SQL-ORDERBYCLAUSE-2">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    ORDER BY clause
   </title>
   <para>
    <synopsis>
ORDER BY <replaceable class="PARAMETER">column</replaceable> [ASC | DESC] [, ...]
    </synopsis></para>
    
   <para>
    <replaceable class="PARAMETER">column</replaceable> can be either a column
    name or an ordinal number.</para>
   <para>
    The ordinal numbers refers to the ordinal (left-to-right) position
    of the 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 assign a name
    to a calculated column using the AS clause, e.g.:
    <programlisting>
     SELECT title, date_prod + 1 AS newlen FROM films ORDER BY newlen;
    </programlisting></para>
    
   <para>
    The columns in the ORDER BY must appear in the SELECT clause.
    Thus the following statement is illegal:
    <programlisting>
     SELECT name FROM distributors ORDER BY code;
    </programlisting></para>
    
   <para>
    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.</para>
  </refsect2>
  
  <refsect2 id="R2-SQL-UNION-2">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    UNION clause
   </title>
   <para>
    <synopsis>
<replaceable class="PARAMETER">table_query</replaceable> UNION [ALL] <replaceable class="PARAMETER">table_query</replaceable>
     [ORDER BY <replaceable class="PARAMETER">column</replaceable> [ASC | DESC] [, ...] ]
    </synopsis>
    
    where
    <replaceable class="PARAMETER">table_query</replaceable>
    specifies any select expression without an ORDER BY clause.</para>
    
   <para>
    The UNION operator specifies a table derived from a Cartesian product.
    The two tables that represent the direct operands of the UNION must
    have the same number of columns, and corresponding columns must be
    of compatible data types.</para>
    
   <para>
    By default, the result of UNION does not contain any duplicate rows
    unless the ALL clause is specified.</para>
    
   <para>
    Multiple UNION operators in the same SELECT statement are evaluated left to right.
    Note that the ALL keyword is not global in nature, being applied only for the current pair of
    table results.</para>
    
  </refsect2></refsect1>
  
 <refsect1 id="R1-SQL-SELECT-2">
  <title>
   Usage
  </title>
  <para>
   To join the table <literal>films</literal> with the table
   <literal>distributors</literal>:
  </para>
  <programlisting>
    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
  </programlisting>
  <para>
   To sum the column <literal>len</literal> of all films and group
   the reults by <literal>kind</literal>:
  </para>
  <programlisting>
    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
  </programlisting>

  <para>
   To sum the column <literal>len</literal> of all films, group
   the reults by <literal>kind</literal> and show those group totals
   that are less than 5 hours:
  </para>
  <programlisting>
    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
  </programlisting>
  <para>
    The following two examples are identical ways of sorting the individual
   results according to the contents of the second column
   (<literal>name</literal>):
  </para>
  <programlisting>
    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
  </programlisting>

  <para>
   This example shows how to obtain the union of the tables
   <literal>distributors</literal> and
   <literal>actors</literal>, restricting the results to those that begin
   with letter W in each table.  Only distinct rows are to be used, so the
   ALL keyword is omitted:
  </para>
  <programlisting>
    --        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
  </programlisting>
  
 </refsect1>
 
 <refsect1 id="R1-SQL-SELECT-3">
  <title>
   Compatibility
  </title>
  <para>
  </para>
  
  <refsect2 id="R2-SQL-SELECT-4">
   <refsect2info>
    <date>1998-09-06</date>
   </refsect2info>
   <title>
    <acronym>SQL92</acronym>
   </title>
   <para>
   </para>
   
   <refsect3 id="R3-SQL-SELECT-1">
    <refsect3info>
     <date>1998-04-15</date>
    </refsect3info>
    <title>
     SELECT clause
    </title>
    <para>
     In the <acronym>SQL92</acronym> standard, the optional keyword "AS"
     is just noise and can be 
     omitted without affecting the meaning.
     The <productname>Postgres</productname> parser requires this keyword when
     renaming columns because the type extensibility features lead to
     parsing ambiguities
     in this context.</para>
     
    <para>
     In the <acronym>SQL92</acronym> standard, the new column name 
     specified in an
     "AS" clause may be referenced in GROUP BY and HAVING clauses.
     This is not currently
     allowed in <productname>Postgres</productname>.
    </para>
   </refsect3>

   <refsect3 id="R3-SQL-UNION-1">
    <refsect3info>
     <date>1998-09-06</date>
    </refsect3info>
    <title>
     UNION clause
    </title>
    <para>
     The <acronym>SQL92</acronym> syntax for UNION allows an
     additional CORRESPONDING BY clause:
     <synopsis> 
<replaceable class="PARAMETER">table_query</replaceable> UNION [ALL]
    [CORRESPONDING [BY (<replaceable class="PARAMETER">column</replaceable> [,...])]]
    <replaceable class="PARAMETER">table_query</replaceable>
     </synopsis></para>

    <para>
     The CORRESPONDING BY clause is not supported by
     <productname>Postgres</productname>.
    </para>
   </refsect3>
   
  </refsect2>
 </refsect1>
</refentry>

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