diff options
| -rw-r--r-- | doc/src/sgml/sql.sgml | 84 |
1 files changed, 42 insertions, 42 deletions
diff --git a/doc/src/sgml/sql.sgml b/doc/src/sgml/sql.sgml index 6f0e4dcb21e..5a2ce9ab015 100644 --- a/doc/src/sgml/sql.sgml +++ b/doc/src/sgml/sql.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/sql.sgml,v 1.16 2001/01/09 15:48:18 momjian Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/sql.sgml,v 1.17 2001/01/09 16:05:21 momjian Exp $ --> <chapter id="sql"> @@ -1058,10 +1058,20 @@ select sname, pname from supplier item that occurs in a FROM clause and before any WHERE, GROUP BY, or HAVING clause. Other table references, including table names or other JOIN clauses, may be included in the FROM clause if separated - by commas. A JOIN of two tables is logically like any other - table listed in the FROM clause. A JOINed table can only be JOINed - to additional tables in a Qualified JOIN as indicated by the - elipses below. + by commas. JOINed tables are logically like any other + table listed in the FROM clause. + </para> + + <para> + JOINs of all types can be chained together or nested where either or both of + <replaceable class="parameter">T1</replaceable> and + <replaceable class="parameter">T2</replaceable> may be JOINed tables. + A Qualified JOIN may be JOINed to another table (or JOINed table) + following its join specification, which consists of either an + ON <replaceable>search condition</replaceable> or + USING ( <replaceable>join column list</replaceable> ) clause. + Parenthesis can be used around JOIN clauses to control the order + of JOINs which are otherwise processed left to right. </para> <variablelist> @@ -1081,37 +1091,35 @@ select sname, pname from supplier respectively, and returns a joined table containing a cross product, NxM, of joined rows. For each row R1 of T1, each row R2 of T2 is joined with R1 to yield a joined table row JR - consisting of all fields in R1 and R2. + consisting of all fields in R1 and R2. A CROSS JOIN is + essentially an INNER JOIN ON TRUE. </para> </listitem> </varlistentry> <varlistentry> - <term>Qualified JOINs</term> + <term>Qualified JOINs</term> <listitem> + <cmdsynopsis> <arg choice="req"> <replaceable class="parameter">T1</replaceable> </arg> - <arg> - <group> - <arg choice="plain"> INNER </arg> + <group choice="opt"> + <arg choice="opt"> INNER </arg> <arg> - <group> - <arg> LEFT </arg> - <arg> RIGHT </arg> - <arg> FULL </arg> + <group choice="req"> + <arg choice="plain"> LEFT </arg> + <arg choice="plain"> RIGHT </arg> + <arg choice="plain"> FULL </arg> </group> - <arg> OUTER </arg> + <arg choice="opt"> OUTER </arg> </arg> - </group> - </arg> + </group> <command> JOIN </command> <arg choice="req"> <replaceable class="parameter">T2</replaceable> </arg> - <arg choice="req"> - <group> + <group choice="req"> <arg> ON <replaceable>search condition</replaceable></arg> <arg> USING ( <replaceable>join column list</replaceable> ) </arg> - </group> - </arg> + </group> <arg choice="plain"> ... </arg> </cmdsynopsis> @@ -1122,9 +1130,6 @@ select sname, pname from supplier column names, which the joined tables must have in common, and joins the tables on those columns, resulting in a joined table having one column for each common column and all of the other columns from both tables. - Like all SELECT queries, the <replaceable>select list</replaceable> of the - SELECT query, before the FROM clause, decides which columns from the joined - table are in the result table returned. </para> <!-- begin join semantics --> @@ -1226,23 +1231,22 @@ select sname, pname from supplier <varlistentry> <term>NATURAL JOINs</term> <listitem> + <cmdsynopsis> <arg choice="req"> <replaceable class="parameter">T1</replaceable> </arg> - <arg> - <arg choice="plain"> NATURAL </arg> - <group> - <arg choice="plain"> INNER </arg> + <arg choice="plain"> NATURAL </arg> + <group choice="opt"> + <arg choice="opt"> INNER </arg> <arg> - <group> - <arg> LEFT </arg> - <arg> RIGHT </arg> - <arg> FULL </arg> + <group choice="req"> + <arg choice="plain"> LEFT </arg> + <arg choice="plain"> RIGHT </arg> + <arg choice="plain"> FULL </arg> </group> - <arg> OUTER </arg> + <arg choice="opt"> OUTER </arg> </arg> - </group> - </arg> - <command> JOIN </command> + </group> + <command> JOIN </command> <arg choice="req"> <replaceable class="parameter">T2</replaceable> </arg> </cmdsynopsis> @@ -1250,18 +1254,14 @@ select sname, pname from supplier A natural join creates a joined table where every pair of matching column names between the two tables are merged into one column. The join specification is effectively a USING clause containing all the - common column names and is otherwise like a Qualified JOIN except - additional JOINs to the JOINed table are not permitted. + common column names and is otherwise like a Qualified JOIN. </para> </listitem> </varlistentry> - <varlistentry> - <term>UNION JOIN</term> - <listitem><para>Deprecated.</para></listitem> - </varlistentry> </variablelist> + </sect3> <sect3> |