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Attached is a doc patch for doc/src/sgml/sql.sgml.
It adds information about SQL JOIN that is implemented in 7.1. -- -------- Robert B. Easter
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‎doc/src/sgml/sql.sgml

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<!--
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$Header: /cvsroot/pgsql/doc/src/sgml/sql.sgml,v 1.15 2000/12/12 05:07:58 tgl Exp $
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$Header: /cvsroot/pgsql/doc/src/sgml/sql.sgml,v 1.16 2001/01/09 15:48:18 momjian Exp $
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-->
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<chapter id="sql">
@@ -1029,6 +1029,239 @@ SELECT S.SNAME, P.PNAME
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named attributes have to be equal). Finally we project out all
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columns but S.SNAME and P.PNAME.
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</para>
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<para>
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Another way to perform joins is to use the SQL JOIN syntax as follows:
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<programlisting>
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select sname, pname from supplier
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JOIN sells USING (sno)
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JOIN part USING (pno);
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</programlisting>
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giving again:
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<programlisting>
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sname | pname
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-------+-------
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Smith | Screw
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Adams | Screw
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Smith | Nut
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Blake | Nut
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Adams | Bolt
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Blake | Bolt
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Jones | Cam
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Blake | Cam
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(8 rows)
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</programlisting>
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</para>
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<para>
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A joined table, created using JOIN syntax, is a table reference list
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item that occurs in a FROM clause and before any WHERE, GROUP BY,
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or HAVING clause. Other table references, including table names or
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other JOIN clauses, may be included in the FROM clause if separated
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by commas. A JOIN of two tables is logically like any other
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table listed in the FROM clause. A JOINed table can only be JOINed
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to additional tables in a Qualified JOIN as indicated by the
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elipses below.
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</para>
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<variablelist>
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<title>Join Types</title>
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<varlistentry>
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<term>CROSS JOIN</term>
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<listitem>
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<cmdsynopsis>
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<arg choice="req"> <replaceable class="parameter">T1</replaceable> </arg>
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<arg choice="plain">CROSS</arg>
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<command> JOIN </command>
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<arg choice="req"> <replaceable class="parameter">T2</replaceable> </arg>
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</cmdsynopsis>
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<para>
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A cross join takes two tables T1 and T2 having N and M rows
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respectively, and returns a joined table containing a cross
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product, NxM, of joined rows. For each row R1 of T1, each row
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R2 of T2 is joined with R1 to yield a joined table row JR
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consisting of all fields in R1 and R2.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Qualified JOINs</term>
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<listitem>
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<cmdsynopsis>
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<arg choice="req"> <replaceable class="parameter">T1</replaceable> </arg>
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<arg>
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<group>
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<arg choice="plain"> INNER </arg>
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<arg>
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<group>
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<arg> LEFT </arg>
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<arg> RIGHT </arg>
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<arg> FULL </arg>
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</group>
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<arg> OUTER </arg>
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</arg>
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</group>
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</arg>
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<command> JOIN </command>
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<arg choice="req"> <replaceable class="parameter">T2</replaceable> </arg>
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<arg choice="req">
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<group>
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<arg> ON <replaceable>search condition</replaceable></arg>
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<arg> USING ( <replaceable>join column list</replaceable> ) </arg>
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</group>
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</arg>
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<arg choice="plain"> ... </arg>
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</cmdsynopsis>
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<para>
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Only the qualified JOIN types can use ON or USING clauses. The ON clause
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takes a <replaceable>search condition</replaceable>, which is the same
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as in a WHERE clause. The USING clause takes a comma-separated list of
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column names, which the joined tables must have in common, and joins
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the tables on those columns, resulting in a joined table having one
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column for each common column and all of the other columns from both tables.
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Like all SELECT queries, the <replaceable>select list</replaceable> of the
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SELECT query, before the FROM clause, decides which columns from the joined
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table are in the result table returned.
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</para>
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<!-- begin join semantics -->
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<variablelist>
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<varlistentry>
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<term>
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<cmdsynopsis>
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<arg> INNER </arg>
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<command> JOIN </command>
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</cmdsynopsis>
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</term>
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<listitem>
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<para>
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For each row R1 of T1, the joined table has a row for each row
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in T2 that satisfies the join specification with R1.
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</para>
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<tip>
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<para>
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The words INNER and OUTER are optional for all JOINs.
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INNER is the default. LEFT, RIGHT, and FULL are for
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OUTER JOINs only.
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</para>
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</tip>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<cmdsynopsis>
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<arg choice="plain"> LEFT </arg>
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<arg> OUTER </arg>
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<command> JOIN </command>
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</cmdsynopsis>
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</term>
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<listitem>
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<para>
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First, an INNER JOIN is performed.
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Then, where a row in T1 does not satisfy the join specification
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with any row in T2, a joined row is returned with null fields in
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columns from T2.
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</para>
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<tip>
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<para>
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The joined table unconditionally has a row for each row in T1.
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</para>
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</tip>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<cmdsynopsis>
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<arg choice="plain"> RIGHT </arg>
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<arg> OUTER </arg>
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<command> JOIN </command>
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</cmdsynopsis>
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</term>
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<listitem>
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<para>
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Rule 1: For each row R2 of T2, the joined table has a row for each
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row in T1 that satisfies the join specification with R2 (transposed
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[INNER] JOIN).
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Rule 2: Where a row in T2 does not satisfy the join specification
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with any row in T1, a joined row is returned with null fields in
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columns from T1.
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</para>
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<tip>
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<para>
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The joined table unconditionally has a row for each row in T2.
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</para>
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</tip>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<cmdsynopsis>
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<arg choice="plain"> FULL </arg>
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<arg> OUTER </arg>
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<command> JOIN </command>
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</cmdsynopsis>
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</term>
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<listitem>
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<para>
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First, a LEFT [OUTER] JOIN is performed.
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Then, Rule 2 of a RIGHT [OUTER] JOIN is performed.
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</para>
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<tip>
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<para>
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The joined table unconditionally has a row for every row of T1
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and a row for every row of T2.
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</para>
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</tip>
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</listitem>
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</varlistentry>
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</variablelist>
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<!-- end join semantics -->
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>NATURAL JOINs</term>
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<listitem>
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<cmdsynopsis>
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<arg choice="req"> <replaceable class="parameter">T1</replaceable> </arg>
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<arg>
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<arg choice="plain"> NATURAL </arg>
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<group>
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<arg choice="plain"> INNER </arg>
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<arg>
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<group>
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<arg> LEFT </arg>
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<arg> RIGHT </arg>
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<arg> FULL </arg>
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</group>
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<arg> OUTER </arg>
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</arg>
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</group>
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</arg>
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<command> JOIN </command>
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<arg choice="req"> <replaceable class="parameter">T2</replaceable> </arg>
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</cmdsynopsis>
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<para>
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A natural join creates a joined table where every pair of matching
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column names between the two tables are merged into one column. The
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join specification is effectively a USING clause containing all the
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common column names and is otherwise like a Qualified JOIN except
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additional JOINs to the JOINed table are not permitted.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>UNION JOIN</term>
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<listitem><para>Deprecated.</para></listitem>
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</varlistentry>
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</variablelist>
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</sect3>
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<sect3>

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