-<!-- $PostgreSQL: pgsql/doc/src/sgml/advanced.sgml,v 1.51 2006/09/16 00:30:11 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/advanced.sgml,v 1.52 2006/10/21 23:12:57 tgl Exp $ -->
<chapter id="tutorial-advanced">
<title>Advanced Features</title>
type of the column <structfield>name</structfield> is
<type>text</type>, a native <productname>PostgreSQL</productname>
type for variable length character strings. State capitals have
- an extra column, state, that shows their state. In
+ an extra column, <structfield>state</>, that shows their state. In
<productname>PostgreSQL</productname>, a table can inherit from
zero or more other tables.
</para>
-<!-- $PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.47 2006/09/16 00:30:15 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.48 2006/10/21 23:12:57 tgl Exp $ -->
<chapter id="tutorial-sql">
<title>The <acronym>SQL</acronym> Language</title>
<para>
In the examples that follow, we assume that you have created a
database named <literal>mydb</literal>, as described in the previous
- chapter, and have
started <application>psql</application>.
+ chapter, and have
been able to start <application>psql</application>.
</para>
<para>
</screen>
This creates the scripts and compiles the C files containing user-defined
- functions and types. (You must use GNU make for this — it may be named
- something different on your system, often <application>gmake</>.)
+ functions and types. (If you installed a pre-packaged version of
+ <productname>PostgreSQL</productname> rather than building from source,
+ look for a directory named <filename>tutorial</> within the
+ <productname>PostgreSQL</productname> documentation. The <quote>make</>
+ part should already have been done for you.)
Then, to start the tutorial, do the following:
<screen>
-<prompt>$</prompt> <userinput>cd <replaceable>....</replaceable>/src/tutorial</userinput>
+<prompt>$</prompt> <userinput>cd <replaceable>....</replaceable>/tutorial</userinput>
<prompt>$</prompt> <userinput>psql -s mydb</userinput>
<computeroutput>
...
In some database systems, including older versions of
<productname>PostgreSQL</productname>, the implementation of
<literal>DISTINCT</literal> automatically orders the rows and
- so <literal>ORDER BY</literal> is redundant. But this is not
+ so <literal>ORDER BY</literal> is unnecessary. But this is not
required by the SQL standard, and current
<productname>PostgreSQL</productname> doesn't guarantee that
<literal>DISTINCT</literal> causes the rows to be ordered.
<para>
Since the columns all had different names, the parser
- automatically found out which table they belong to, but it is good
- style to fully qualify column names in join queries:
+ automatically found out which table they belong to. If there
+ were duplicate column names in the two tables you'd need to
+ <firstterm>qualify</> the column names to show which one you
+ meant, as in:
<programlisting>
SELECT weather.city, weather.temp_lo, weather.temp_hi,
FROM weather, cities
WHERE cities.name = weather.city;
</programlisting>
+
+ It is widely considered good style to qualify all column names
+ in a join query, so that the query won't fail if a duplicate
+ column name is later added to one of the tables.
</para>
<para>
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. If no matching row is
+ matching <classname>cities</classname> 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
of query is called an <firstterm>outer join</firstterm>. (The
but this will not work since the aggregate
<function>max</function> cannot be used in the
<literal>WHERE</literal> clause. (This restriction exists because
- the <literal>WHERE</literal> clause determines the rows that will
- go into the aggregation stage; so it has to be evaluated before
- aggregate functions are computed.)
+ the <literal>WHERE</literal> clause determines which rows will be
+ included in the aggregate calculation; so obviously 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 desired result, here
by using a <firstterm>subquery</firstterm>:
<programlisting>
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 after November 28. You may correct the
data as follows:
<programlisting>
-<!-- $PostgreSQL: pgsql/doc/src/sgml/start.sgml,v 1.42 2006/09/16 00:30:15 momjian Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/start.sgml,v 1.43 2006/10/21 23:12:57 tgl Exp $ -->
<chapter id="tutorial-start">
<title>Getting Started</title>
<para>
Another response could be this:
<screen>
-createdb: could not connect to database postgres: could not connect to server:
-No such file or directory
+createdb: could not connect to database postgres: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
</screen>
<para>
Another response could be this:
<screen>
-createdb: could not connect to database postgres: FATAL: user "joe" does not
-exist
+createdb: could not connect to database postgres: FATAL: role "joe" does not exist
</screen>
where your own login name is mentioned. This will happen if the
administrator has not created a <productname>PostgreSQL</> user account
<para>
As an explanation for why this works:
<productname>PostgreSQL</productname> user names are separate
- from operating system user accounts. If you connect to a
+ from operating system user accounts. When you connect to a
database, you can choose what
<productname>PostgreSQL</productname> user name to connect as;
if you don't, it will default to the same name as your current
That would mean you are a database superuser, which is most likely
the case if you installed <productname>PostgreSQL</productname>
yourself. Being a superuser means that you are not subject to
- access controls. For the purpose of this tutorial this is not of
+ access controls. For the purposes of this tutorial that is not of
importance.
</para>
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