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<chapter id="functions">

<title>Functions and Operators</title>

<entry>

array of the argument type

</entry>

<entry>input values concatenated into an array</entry>

<entry>input values, including nulls, concatenated into an array</entry>

</row>

<row>

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<chapter id="sql-syntax">

<title>SQL Syntax</title>

<para>

The first form of aggregate expression invokes the aggregate

across all input rows for which the given expression(s) yield

non-null values. (Actually, it is up to the aggregate function

whether to ignore null values or not &mdash; but all the standard ones do.)

once for each input row.

The second form is the same as the first, since

<literal>ALL</literal> is the default. The third form invokes the

in theinput rows (ignoring nulls if the function chooses to do so).

The last form invokestheaggregate once for

each input row regardless of null or non-null values; since no

<literal>ALL</literal> is the default.

of theexpression (or distinct set of values, for multiple expressions)

found intheinput rows.

The last form invokes the aggregate once for each input row; since no

particular input value is specified, it is generally only useful

for the <function>count(*)</function> aggregate function.

</para>

<para>

Most aggregate functions ignore null inputs, so that rows in which

one or more of the expression(s) yield null are discarded. This

can be assumed to be true, unless otherwise specified, for all

built-in aggregates.

</para>

<para>

For example, <literal>count(*)</literal> yields the total number

of input rows; <literal>count(f1)</literal> yields the number of

input rows in which <literal>f1</literal> is non-null;

input rows in which <literal>f1</literal> is non-null, since

<function>count</> ignores nulls; and

<literal>count(distinct f1)</literal> yields the number of

distinct non-null values of <literal>f1</literal>.

</para>