Add a few more cross-references where appropriate, add more text about
the FROM clause and an example to the UPDATE reference page, and make a few other SGML tweaks.
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Neil Conway
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<!-- $PostgreSQL: pgsql/doc/src/sgml/queries.sgml,v 1.28 2003/11/29 19:51:37 pgsql Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/queries.sgml,v 1.29 2004/03/03 22:22:24 neilc Exp $ -->
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<chapter id="queries">
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<title>Queries</title>
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@ -108,8 +108,9 @@ SELECT random();
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<title>The <literal>FROM</literal> Clause</title>
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<para>
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The <literal>FROM</> clause derives a table from one or more other
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tables given in a comma-separated table reference list.
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The <xref linkend="sql-from" endterm="sql-from-title"> derives a
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table from one or more other tables given in a comma-separated
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table reference list.
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<synopsis>
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FROM <replaceable>table_reference</replaceable> <optional>, <replaceable>table_reference</replaceable> <optional>, ...</optional></optional>
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</synopsis>
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@ -677,7 +678,8 @@ SELECT *
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</indexterm>
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<para>
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The syntax of the <literal>WHERE</> clause is
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The syntax of the <xref linkend="sql-where"
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endterm="sql-where-title"> clause is
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<synopsis>
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WHERE <replaceable>search_condition</replaceable>
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</synopsis>
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@ -783,13 +785,14 @@ SELECT <replaceable>select_list</replaceable>
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</synopsis>
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<para>
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The <literal>GROUP BY</> clause is used to group together those rows in
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a table that share the same values in all the columns listed. The
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order in which the columns are listed does not matter. The
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purpose is to reduce each group of rows sharing common values into
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one group row that is representative of all rows in the group.
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This is done to eliminate redundancy in the output and/or compute
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aggregates that apply to these groups. For instance:
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The <xref linkend="sql-groupby" endterm="sql-groupby-title"> is
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used to group together those rows in a table that share the same
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values in all the columns listed. The order in which the columns
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are listed does not matter. The purpose is to reduce each group
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of rows sharing common values into one group row that is
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representative of all rows in the group. This is done to
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eliminate redundancy in the output and/or compute aggregates that
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apply to these groups. For instance:
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<screen>
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<prompt>=></> <userinput>SELECT * FROM test1;</>
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x | y
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@ -1058,7 +1061,7 @@ SELECT a AS value, b + c AS sum FROM ...
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<synopsis>
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SELECT DISTINCT <replaceable>select_list</replaceable> ...
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</synopsis>
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(Instead of <literal>DISTINCT</> the word <literal>ALL</literal>
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(Instead of <literal>DISTINCT</> the key word <literal>ALL</literal>
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can be used to select the default behavior of retaining all rows.)
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</para>
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.74 2003/12/14 00:15:03 neilc Exp $
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$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.75 2004/03/03 22:22:24 neilc Exp $
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PostgreSQL documentation
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-->
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@ -174,7 +174,8 @@ where <replaceable class="parameter">from_item</replaceable> can be one of:
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</para>
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<para>
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<literal>FROM</literal>-clause elements can contain:
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The <literal>FROM</literal> clause can contain the following
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elements:
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<variablelist>
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<varlistentry>
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@ -289,16 +290,16 @@ where <replaceable class="parameter">from_item</replaceable> can be one of:
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A <literal>JOIN</literal> clause combines two
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<literal>FROM</> items. Use parentheses if necessary to
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determine the order of nesting. In the absence of parentheses,
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<literal>JOIN</literal>s nest left-to-right. In any case
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<literal>JOIN</literal> binds more tightly than the commas
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separating <literal>FROM</> items.
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<literal>JOIN</literal>s nest left-to-right. In any case
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<literal>JOIN</literal> binds more tightly than the commas
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separating <literal>FROM</> items.
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</para>
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<para>
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<literal>CROSS JOIN</> and <literal>INNER JOIN</literal>
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produce a simple Cartesian product, the same result as you get from
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listing the two items at the top level of <literal>FROM</>,
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but restricted by the join condition (if any).
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but restricted by the join condition (if any).
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<literal>CROSS JOIN</> is equivalent to <literal>INNER JOIN ON
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(TRUE)</>, that is, no rows are removed by qualification.
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These join types are just a notational convenience, since they
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@ -647,7 +648,7 @@ SELECT name FROM distributors ORDER BY code;
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<literal>INTERSECT</>, or <literal>EXCEPT</> clause may only
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specify an output column name or number, not an expression.
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</para>
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<para>
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If an <literal>ORDER BY</> expression is a simple name that
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matches both a result column name and an input column name,
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.27 2003/11/29 19:51:39 pgsql Exp $
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$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.28 2004/03/03 22:22:24 neilc Exp $
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PostgreSQL documentation
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-->
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@ -32,8 +32,8 @@ UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> SET <replacea
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<para>
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<command>UPDATE</command> changes the values of the specified
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columns in all rows that satisfy the condition. Only the columns to
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be modified need be mentioned in the statement; columns not explicitly
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<literal>SET</> retain their previous values.
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be modified need be mentioned in the <literal>SET</literal> clause;
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columns not explicitly modified retain their previous values.
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</para>
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<para>
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@ -43,6 +43,14 @@ UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> SET <replacea
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clause.
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</para>
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<para>
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There are two ways to modify a table using information contained in
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other tables in the database: using sub-selects, or specifying
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additional tables in the <literal>FROM</literal> clause. Which
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technique is more appropriate depends on the specific
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circumstances.
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</para>
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<para>
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You must have the <literal>UPDATE</literal> privilege on the table
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to update it, as well as the <literal>SELECT</literal>
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@ -99,7 +107,12 @@ UPDATE [ ONLY ] <replaceable class="PARAMETER">table</replaceable> SET <replacea
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<listitem>
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<para>
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A list of table expressions, allowing columns from other tables
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to appear in the <literal>WHERE</> condition and the update expressions.
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to appear in the <literal>WHERE</> condition and the update
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expressions. This is similar to the list of tables that can be
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specified in the <xref linkend="sql-from"
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endterm="sql-from-title"> of a <command>SELECT</command>
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statement; for example, an alias for the table name can be
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specified.
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</para>
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</listitem>
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</varlistentry>
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@ -139,7 +152,7 @@ UPDATE <replaceable class="parameter">count</replaceable>
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<para>
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Change the word <literal>Drama</> to <literal>Dramatic</> in the
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column <structfield>kind</> of the table <literal>films</literal>:
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column <structfield>kind</> of the table <structname>films</structname>:
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<programlisting>
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UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';
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@ -148,7 +161,7 @@ UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';
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<para>
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Adjust temperature entries and reset precipitation to its default
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value in one row of the table <literal>weather</literal>:
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value in one row of the table <structname>weather</structname>:
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<programlisting>
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UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
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@ -156,13 +169,30 @@ UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
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</programlisting>
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</para>
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<para>
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Increment the sales count of the salesperson who manages the
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account for Acme Corporation, using the <literal>FROM</literal>
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clause syntax:
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<programlisting>
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UPDATE employees SET sales_count = sales_count + 1 FROM accounts
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WHERE accounts.name = 'Acme Corporation'
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AND employees.id = accounts.sales_person;
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</programlisting>
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Perform the same operation, using a sub-select in the
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<literal>WHERE</literal> clause:
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<programlisting>
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UPDATE employees SET sales_count = sales_count + 1 WHERE id =
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(SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');
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</programlisting>
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</para>
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</refsect1>
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<refsect1>
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<title>Compatibility</title>
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<para>
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This command conforms to the SQL standard. The
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This command conforms to the <acronym>SQL</acronym> standard. The
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<literal>FROM</literal> clause is a
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<productname>PostgreSQL</productname> extension.
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</para>
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@ -1,5 +1,5 @@
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<!--
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$PostgreSQL: pgsql/doc/src/sgml/trigger.sgml,v 1.34 2004/01/22 19:50:21 neilc Exp $
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$PostgreSQL: pgsql/doc/src/sgml/trigger.sgml,v 1.35 2004/03/03 22:22:24 neilc Exp $
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-->
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<chapter id="triggers">
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@ -449,9 +449,9 @@ typedef struct Trigger
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<para>
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The function <function>trigf</> reports the number of rows in the
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table <literal>ttest</> and skips the actual operation if the
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table <structname>ttest</> and skips the actual operation if the
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command attempts to insert a null value into the column
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<literal>x</>. (So the trigger acts as a not-null constraint but
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<structfield>x</>. (So the trigger acts as a not-null constraint but
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doesn't abort the transaction.)
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</para>
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