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<chapter id="advanced">

Here the <quote>*</quote> after cities indicates that the query should

be run over cities and all classes below cities in the

inheritance hierarchy. Many of the commands that we

have already discussed (<command>select</command>,

<command>update</command> and <command>delete</command>)

have already discussed (<command>SELECT</command>,

<command>UPDATE</command> and <command>DELETE</command>)

support this <quote>*</quote> notation, as do others, like

<command>alter</command>.

<command>ALTER</command>.

</para>

</sect1>

<para>

One of the tenets of the relational model is that the

attributes of a relation are atomic. <productname>Postgres</productname> does not

attributes of a relation are atomic.

<productname>Postgres</productname> does not

have this restriction; attributes can themselves contain

sub-values that can be accessed from the query

language. For example, you can create attributes that

<title>Arrays</title>

<para>

<productname>Postgres</productname> allows attributes of an instance to be defined

<productname>Postgres</productname> allows attributes of an

instance to be defined

as fixed-length or variable-length multi-dimensional

arrays. Arrays of any base type or user-defined type

can be created. To illustrate their use, we first create a

a <firstterm>text</firstterm> string (name), a one-dimensional

array of <firstterm>int4</firstterm>

(pay_by_quarter), which represents the employee's

salary by quarter and a two-dimensional array of <firstterm>text</firstterm>

salary by quarter and a two-dimensional array of

<firstterm>text</firstterm>

(schedule), which represents the employee's weekly

schedule. Now we do some <firstterm>INSERTS</firstterm>s; note that when

schedule. Now we do some <firstterm>INSERTS</firstterm>s;

note that when

appending to an array, we enclose the values within

braces and separate them by commas. If you know <firstterm>C</firstterm>,

braces and separate them by commas. If you know

<firstterm>C</firstterm>,

this is not unlike the syntax for initializing structures.

<programlisting>

'{{"talk", "consult"}, {"meeting"}}');

</programlisting>

By default, <productname>Postgres</productname> uses the "one-based" numbering

By default, <productname>Postgres</productname> uses the

"one-based" numbering

convention for arrays -- that is, an array of n elements

starts with array[1] and ends with array[n].

Now, we can run some queries on SAL_EMP. First, we

</sect2>

</sect1>

<!--

We haven't had Time Travel for two or three years, so let's stop

mentioning it. - thomas 2000-04-02

<sect1>

<title>Time Travel</title>

</para>

<para>

New features such as triggers allow one to mimic the behavior of time travel when desired, without

incurring the overhead when it is not needed (for most users, this is most of the time).

See examples in the <filename>contrib</filename> directory for more information.

New features such as triggers allow one to mimic the behavior of

time travel when desired, without

incurring the overhead when it is not needed (for most users, this

is most of the time).

See examples in the <filename>contrib</filename> directory for

more information.

</para>

<note>

<title>Time travel is deprecated</title>

<para>

The remaining text in this section is retained only until it can be rewritten in the context

of new techniques to accomplish the same purpose. Volunteers? - thomas 1998-01-12

The remaining text in this section is retained only until it can

be rewritten in the context

of new techniques to accomplish the same purpose.

Volunteers? - thomas 1998-01-12

</para>

</note>

<para>

<productname>Postgres</productname> supports the notion of time travel. This feature

<productname>Postgres</productname> supports the notion of time

travel. This feature

allows a user to run historical queries. For

example, to find the current population of Mariposa

city, one would query:

+---------+------------+----------+

</programlisting>

<productname>Postgres</productname> will automatically find the version of Mariposa's

<productname>Postgres</productname> will automatically find the

version of Mariposa's

record valid at the current time.

One can also give a time range. For example to see the

past and present populations of Mariposa, one would

abbreviated as ``[,].''

</para>

</sect1>

-->

<sect1>

<title>More Advanced Features</title>

<para>

<productname>Postgres</productname> has many features not touched upon in this

<productname>Postgres</productname> has many features not touched

upon in this

tutorial introduction, which has been oriented toward newer users of

<acronym>SQL</acronym>.

These are discussed in more detail in both the User's and Programmer's Guides.

These are discussed in more detail in both the User's and

Programmer's Guides.

</para>

</sect1>

</chapter>

<!-- Keep this comment at the end of the file

<entry>abs(-17.4)</entry>

</row>

<row>

<entry>sqrt(float8)</entry>

<entry>degrees(float8)</entry>

<entry>float8</entry>

<entry>square root</entry>

<entry>sqrt(2.0)</entry>

<entry>radians to degrees</entry>

<entry>degrees(0.5)</entry>

</row>

<row>

<entry>exp(float8)</entry>

<entry>base 10 logarithm</entry>

<entry>log(2.0)</entry>

</row>

<row>

<entry>pi()</entry>

<entry>float8</entry>

<entry>fundamental constant</entry>

<entry>pi()</entry>

</row>

<row>

<entry>pow(float8,float8)</entry>

<entry>float8</entry>

<entry>raise a number to the specified exponent</entry>

<entry>pow(2.0, 16.0)</entry>

</row>

<row>

<entry>radians(float8)</entry>

<entry>float8</entry>

<entry>degrees to radians</entry>

<entry>radians(45.0)</entry>

</row>

<row>

<entry>round(float8)</entry>

<entry>float8</entry>

<entry>round to nearest integer</entry>

<entry>round(42.4)</entry>

</row>

<row>

<entry>sqrt(float8)</entry>

<entry>float8</entry>

<entry>square root</entry>

<entry>sqrt(2.0)</entry>

</row>

<row>

<entry>trunc(float8)</entry>

<entry>float8</entry>

Most of the functions listed for FLOAT8 are also available for

type NUMERIC.

</para>

<para>

<table tocentry="1">

<title>Transcendental Mathematical Functions</title>

<tgroup cols="4">

<thead>

<row>

<entry>Function</entry>

<entry>Returns</entry>

<entry>Description</entry>

<entry>Example</entry>

</row>

</thead>

<tbody>

<row>

<entry>acos(float8)</entry>

<entry>float8</entry>

<entry>arccosine</entry>

<entry>acos(10.0)</entry>

</row>

<row>

<entry>asin(float8)</entry>

<entry>float8</entry>

<entry>arcsine</entry>

<entry>asin(10.0)</entry>

</row>

<row>

<entry>atan(float8)</entry>

<entry>float8</entry>

<entry>arctangent</entry>

<entry>atan(10.0)</entry>

</row>

<row>

<entry>atan2(float8,float8)</entry>

<entry>float8</entry>

<entry>arctangent</entry>

<entry>atan3(10.0,20.0)</entry>

</row>

<row>

<entry>cos(float8)</entry>

<entry>float8</entry>

<entry>cosine</entry>

<entry>cos(0.4)</entry>

</row>

<row>

<entry>cot(float8)</entry>

<entry>float8</entry>

<entry>cotangent</entry>

<entry>cot(20.0)</entry>

</row>

<row>

<entry>sin(float8)</entry>

<entry>float8</entry>

<entry>sine</entry>

<entry>cos(0.4)</entry>

</row>

<row>

<entry>cos(float8)</entry>

<entry>float8</entry>

<entry>cosine</entry>

<entry>cos(0.4)</entry>

</row>

<row>

<entry>cos(float8)</entry>

<entry>float8</entry>

<entry>cosine</entry>

<entry>cos(0.4)</entry>

</row>

<row>

<entry>cos(float8)</entry>

<entry>float8</entry>

<entry>cosine</entry>

<entry>cos(0.4)</entry>

</row>

<row>

<entry>cos(float8)</entry>

<entry>float8</entry>

<entry>cosine</entry>

<entry>cos(0.4)</entry>

</row>

</sect1>

<sect1>