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PostgreSQL documentation
-->
</para>
</refsect1>
+ <refsect1>
+ <title>Examples</title>
+
+ <para>
+ Create a new table <literal>films_recent</literal> consisting of only
+ recent entries from the table <literal>films</literal>:
+
+<programlisting>
+CREATE TABLE films_recent AS
+ SELECT * FROM films WHERE date_prod >= '2002-01-01';
+</programlisting>
+ </para>
+ </refsect1>
+
<refsect1>
<title>Compatibility</title>
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</para>
</refsect1>
+ <refsect1>
+ <title>Notes</title>
+
+ <para>
+ <productname>PostgreSQL</productname> lets you reference columns of
+ other tables in the <literal>WHERE</> condition. For example, to
+ delete all films produced by a given producer, one might do
+<programlisting>
+DELETE FROM films
+ WHERE producer_id = producers.id AND producers.name = 'foo';
+</programlisting>
+ What is essentially happening here is a join between <structname>films</>
+ and <structname>producers</>, with all successfully joined
+ <structname>films</> rows being marked for deletion.
+ This syntax is not standard. A more standard way to do it is
+<programlisting>
+DELETE FROM films
+ WHERE producer_id IN (SELECT id FROM producers WHERE name = 'foo');
+</programlisting>
+ In some cases the join style is easier to write or faster to
+ execute than the sub-select style. One objection to the join style
+ is that there is no explicit list of what tables are being used,
+ which makes the style somewhat error-prone; also it cannot handle
+ self-joins.
+ </para>
+ </refsect1>
+
<refsect1>
<title>Examples</title>
<title>Compatibility</title>
<para>
- This command conforms to the SQL standard.
+ This command conforms to the SQL standard, except that the ability to
+ reference other tables in the <literal>WHERE</> clause is a
+ <productname>PostgreSQL</productname> extension.
</para>
</refsect1>
</refentry>
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<para>
<command>DROP GROUP</command> removes the specified group. The
- users in the group are not deleted.
+ users in the group are not removed.
</para>
</refsect1>
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</para>
<para>
- In this second example, the <literal>len</literal> column is
+ In this example, the <literal>len</literal> column is
omitted and therefore it will have the default value:
<programlisting>
</para>
<para>
- The third example uses the <literal>DEFAULT</literal> clause for
+ This example uses the <literal>DEFAULT</literal> clause for
the date columns rather than specifying a value:
<programlisting>
</para>
<para>
- This example inserts several rows into table
- <literal>films</literal> from table <literal>tmp</literal>:
+ To insert a row consisting entirely of default values:
<programlisting>
-INSERT INTO films SELECT * FROM tmp;
+INSERT INTO films DEFAULT VALUES;
+</programlisting>
+ </para>
+
+ <para>
+ This example inserts some rows into table
+ <literal>films</literal> from a table <literal>tmp_films</literal>
+ with the same column layout as <literal>films</literal>:
+
+<programlisting>
+INSERT INTO films SELECT * FROM tmp_films WHERE date_prod < '2004-05-07';
</programlisting>
</para>
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PostgreSQL documentation
-->
</para>
</refsect1>
+ <refsect1>
+ <title>Examples</title>
+
+ <para>
+ Create a new table <literal>films_recent</literal> consisting of only
+ recent entries from the table <literal>films</literal>:
+
+<programlisting>
+SELECT * INTO films_recent FROM films WHERE date_prod >= '2002-01-01';
+</programlisting>
+ </para>
+ </refsect1>
+
<refsect1>
<title>Compatibility</title>
new code.
</para>
</refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+
+ <simplelist type="inline">
+ <member><xref linkend="sql-createtableas" endterm="sql-createtableas-title"></member>
+ </simplelist>
+ </refsect1>
</refentry>
<!-- Keep this comment at the end of the file
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-->
expressions. This is similar to the list of tables that can be
specified in the <xref linkend="sql-from"
endterm="sql-from-title"> of a <command>SELECT</command>
- statement; for example, an alias for the table name can be
- specified.
+ statement. Note that the target table must not appear in the
+ <replaceable>fromlist</>, unless you intend a self-join (in which
+ case it must appear with an alias in the <replaceable>fromlist</>).
</para>
</listitem>
</varlistentry>
<title>Notes</title>
<para>
- When joining the target table to other tables using a <replaceable
- class="PARAMETER">fromlist</replaceable>, be careful that the join
+ When a <literal>FROM</> clause is present, what essentially happens
+ is that the target table is joined to the tables mentioned in the
+ <replaceable>fromlist</replaceable>, and each output row of the join
+ represents an update operation for the target table. When using
+ <literal>FROM</> you should ensure that the join
produces at most one output row for each row to be modified. In
- other words, a target row mustn't join to more than one row from
+ other words, a target row shouldn't join to more than one row from
the other table(s). If it does, then only one of the join rows
will be used to update the target row, but which one will be used
is not readily predictable.
</programlisting>
Attempt to insert a new stock item along with the quantity of stock. If
- the item exists, update the stock count of the existing item. To do this,
- use savepoints.
+ the item already exists, instead update the stock count of the existing
+ item. To do this without failing the entire transaction, use savepoints.
<programlisting>
BEGIN;
+-- other operations
SAVEPOINT sp1;
INSERT INTO wines VALUES('Chateau Lafite 2003', '24');
--- Check for unique violation on name
+-- Assume the above fails because of a unique key violation,
+-- so now we issue these commands:
ROLLBACK TO sp1;
-UPDATE wines SET stock = stock + 24 WHERE winename='Chateau Lafite 2003';
+UPDATE wines SET stock = stock + 24 WHERE winename = 'Chateau Lafite 2003';
+-- continue with other operations, and eventually
COMMIT;
</programlisting>
</para>
<title>Compatibility</title>
<para>
- This command conforms to the <acronym>SQL</acronym> standard. The
- <literal>FROM</literal> clause is a
+ This command conforms to the <acronym>SQL</acronym> standard, except
+ that the <literal>FROM</literal> clause is a
<productname>PostgreSQL</productname> extension.
</para>
+
+ <para>
+ Some other database systems offer a <literal>FROM</> option in which
+ the target table is supposed to be listed again within <literal>FROM</>.
+ That is not how <productname>PostgreSQL</productname> interprets
+ <literal>FROM</>. Be careful when porting applications that use this
+ extension.
+ </para>
</refsect1>
</refentry>
projects / postgresql / commitdiff