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Diffstat (limited to 'doc/src/sgml/query.sgml')
| -rw-r--r-- | doc/src/sgml/query.sgml | 39 |
1 files changed, 20 insertions, 19 deletions
diff --git a/doc/src/sgml/query.sgml b/doc/src/sgml/query.sgml index c81c321134b..49a1221ea0f 100644 --- a/doc/src/sgml/query.sgml +++ b/doc/src/sgml/query.sgml @@ -1,4 +1,4 @@ -<!-- $PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.52 2009/04/27 16:27:36 momjian Exp $ --> +<!-- $PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.53 2009/06/17 21:58:49 tgl Exp $ --> <chapter id="tutorial-sql"> <title>The <acronym>SQL</acronym> Language</title> @@ -53,7 +53,7 @@ </screen> The <literal>\i</literal> command reads in commands from the - specified file. The <command>psql</command> <literal>-s</> option puts you in + specified file. <command>psql</command>'s <literal>-s</> option puts you in 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>. @@ -150,7 +150,7 @@ CREATE TABLE weather ( <type>int</type> is the normal integer type. <type>real</type> is a type for storing single precision floating-point numbers. <type>date</type> should be self-explanatory. (Yes, the column of - type <type>date</type> is also named <literal>date</literal>. + type <type>date</type> is also named <structfield>date</structfield>. This might be convenient or confusing — you choose.) </para> @@ -165,7 +165,7 @@ CREATE TABLE weather ( and a rich set of geometric types. <productname>PostgreSQL</productname> can be customized with an arbitrary number of user-defined data types. Consequently, type - names are not special key words in the syntax except where required to + names are not key words in the syntax, except where required to support special cases in the <acronym>SQL</acronym> standard. </para> @@ -291,7 +291,7 @@ COPY weather FROM '/home/user/weather.txt'; tables from which to retrieve the data), and an optional qualification (the part that specifies any restrictions). For example, to retrieve all the rows of table - <classname>weather</classname>, type: + <structname>weather</structname>, type: <programlisting> SELECT * FROM weather; </programlisting> @@ -450,9 +450,10 @@ SELECT DISTINCT city of the same or different tables at one time is called a <firstterm>join</firstterm> query. As an example, say you wish to list all the weather records together with the location of the - associated city. To do that, we need to compare the city column of - each row of the <literal>weather</> table with the name column of all rows in - the <literal>cities</> table, and select the pairs of rows where these values match. + associated city. To do that, we need to compare the <structfield>city</> + column of each row of the <structname>weather</> table with the + <structfield>name</> column of all rows in the <structname>cities</> + table, and select the pairs of rows where these values match. <note> <para> This is only a conceptual model. The join is usually performed @@ -485,8 +486,8 @@ SELECT * <para> There is no result row for the city of Hayward. This is because there is no matching entry in the - <classname>cities</classname> table for Hayward, so the join - ignores the unmatched rows in the <literal>weather</> table. We will see + <structname>cities</structname> table for Hayward, so the join + ignores the unmatched rows in the <structname>weather</> table. We will see shortly how this can be fixed. </para> </listitem> @@ -494,9 +495,9 @@ SELECT * <listitem> <para> There are two columns containing the city name. This is - correct because the columns from the - <classname>weather</classname> and the - <classname>cities</classname> tables are concatenated. In + correct because the lists of columns from the + <structname>weather</structname> and + <structname>cities</structname> tables are concatenated. In practice this is undesirable, though, so you will probably want to list the output columns explicitly rather than using <literal>*</literal>: @@ -556,10 +557,10 @@ SELECT * Now we will figure out how we can get the Hayward records back in. What we want the query to do is to scan the - <classname>weather</classname> table and for each row to find the - matching <classname>cities</classname> row(s). If no matching row is + <structname>weather</structname> table and for each row to find the + matching <structname>cities</structname> row(s). If no matching row is found we want some <quote>empty values</quote> to be substituted - for the <classname>cities</classname> table's columns. This kind + for the <structname>cities</structname> table's columns. This kind of query is called an <firstterm>outer join</firstterm>. (The joins we have seen so far are inner joins.) The command looks like this: @@ -603,10 +604,10 @@ SELECT * to find all the weather records that are in the temperature range of other weather records. So we need to compare the <structfield>temp_lo</> and <structfield>temp_hi</> columns of - each <classname>weather</classname> row to the + each <structname>weather</structname> row to the <structfield>temp_lo</structfield> and <structfield>temp_hi</structfield> columns of all other - <classname>weather</classname> rows. We can do this with the + <structname>weather</structname> rows. We can do this with the following query: <programlisting> @@ -756,7 +757,7 @@ SELECT city, max(temp_lo) </screen> which gives us the same results for only the cities that have all - <literal>temp_lo</> values below 40. Finally, if we only care about + <structfield>temp_lo</> values below 40. Finally, if we only care about cities whose names begin with <quote><literal>S</literal></quote>, we might do: |