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Diffstat (limited to 'doc/src/sgml/query.sgml')
| -rw-r--r-- | doc/src/sgml/query.sgml | 34 |
1 files changed, 21 insertions, 13 deletions
diff --git a/doc/src/sgml/query.sgml b/doc/src/sgml/query.sgml index 1ec9fba7226..4eed42be300 100644 --- a/doc/src/sgml/query.sgml +++ b/doc/src/sgml/query.sgml @@ -1,5 +1,5 @@ <!-- -$Header: /cvsroot/pgsql/doc/src/sgml/query.sgml,v 1.27 2002/10/24 17:48:54 petere Exp $ +$Header: /cvsroot/pgsql/doc/src/sgml/query.sgml,v 1.28 2002/11/11 20:14:03 petere Exp $ --> <chapter id="tutorial-sql"> @@ -13,7 +13,7 @@ $Header: /cvsroot/pgsql/doc/src/sgml/query.sgml,v 1.27 2002/10/24 17:48:54 peter <acronym>SQL</acronym> to perform simple operations. This tutorial is only intended to give you an introduction and is in no way a complete tutorial on <acronym>SQL</acronym>. Numerous books - have been written on <acronym>SQL92</acronym>, including <xref + have been written on <acronym>SQL</acronym>, including <xref linkend="MELT93"> and <xref linkend="DATE97">. You should be aware that some <productname>PostgreSQL</productname> language features are extensions to the standard. @@ -44,7 +44,7 @@ $Header: /cvsroot/pgsql/doc/src/sgml/query.sgml,v 1.27 2002/10/24 17:48:54 peter The <literal>\i</literal> command reads in commands from the specified file. The <literal>-s</literal> option puts you in - single step mode which pauses before sending each query to the + single step mode which pauses before sending each statement to the server. The commands used in this section are in the file <filename>basics.sql</filename>. </para> @@ -502,7 +502,7 @@ SELECT * join operator will have each of its rows in the output at least once, whereas the table on the right will only have those rows output that match some row of the left table. When outputting a - left-table row for which there is no right-table match, empty (NULL) + left-table row for which there is no right-table match, empty (null) values are substituted for the right-table columns. </para> @@ -601,7 +601,7 @@ SELECT max(temp_lo) FROM weather; <para> <indexterm><primary>subquery</primary></indexterm> - If we want to know what city (or cities) that reading occurred in, + If we wanted to know what city (or cities) that reading occurred in, we might try <programlisting> @@ -615,7 +615,7 @@ SELECT city FROM weather WHERE temp_lo = max(temp_lo); <lineannotation>WRONG go into the aggregation stage; so it has to be evaluated before aggregate functions are computed.) However, as is often the case - the query can be restated to accomplish the intended result; here + the query can be restated to accomplish the intended result, here by using a <firstterm>subquery</firstterm>: <programlisting> @@ -630,9 +630,9 @@ SELECT city FROM weather (1 row) </screen> - This is OK because the sub-select is an independent computation + This is OK because the subquery is an independent computation that computes its own aggregate separately from what is happening - in the outer select. + in the outer query. </para> <para> @@ -684,10 +684,18 @@ SELECT city, max(temp_lo) <programlisting> SELECT city, max(temp_lo) FROM weather - WHERE city LIKE 'S%' + WHERE city LIKE 'S%'<co id="co.tutorial-agg-like"> GROUP BY city HAVING max(temp_lo) < 40; </programlisting> + <calloutlist> + <callout arearefs="co.tutorial-agg-like"> + <para> + The <literal>LIKE</literal> operator does pattern matching and + is explained in the &cite-user;. + </para> + </callout> + </calloutlist> </para> <para> @@ -729,7 +737,7 @@ SELECT city, max(temp_lo) You can update existing rows using the <command>UPDATE</command> command. Suppose you discover the temperature readings are - all off by 2 degrees as of November 28, you may update the + all off by 2 degrees as of November 28. You may update the data as follows: <programlisting> @@ -762,8 +770,8 @@ SELECT * FROM weather; </indexterm> <para> - Suppose you are no longer interested in the weather of Hayward, - then you can do the following to delete those rows from the table. + Suppose you are no longer interested in the weather of Hayward. + Then you can do the following to delete those rows from the table. Deletions are performed using the <command>DELETE</command> command: <programlisting> @@ -786,7 +794,7 @@ SELECT * FROM weather; </para> <para> - One should be wary of queries of the form + One should be wary of statements of the form <synopsis> DELETE FROM <replaceable>tablename</replaceable>; </synopsis> |