<function>array_prepend</function>, <function>array_append</function>,

or <function>array_cat</function>. The first two only support one-dimensional

arrays, but <function>array_cat</function> supports multidimensional arrays.

Note that the concatenation operator discussed above is preferred over

direct use of these functions. In fact, these functions primarily exist for use

in implementing the concatenation operator. However, they might be directly

useful in the creation of user-defined aggregates. Some examples:

Some examples:

<programlisting>

SELECT array_prepend(1, ARRAY[2,3]);

{{5,6},{1,2},{3,4}}

</programlisting>

</para>

<para>

In simple cases, the concatenation operator discussed above is preferred

over direct use of these functions. However, because the concatenation

operator is overloaded to serve all three cases, there are situations where

use of one of the functions is helpful to avoid ambiguity. For example

consider:

<programlisting>

SELECT ARRAY[1, 2] || '{3, 4}'; -- the untyped literal is taken as an array

?column?

-----------

{1,2,3,4}

SELECT ARRAY[1, 2] || '7'; -- so is this one

ERROR: malformed array literal: "7"

SELECT ARRAY[1, 2] || NULL; -- so is an undecorated NULL

?column?

----------

{1,2}

(1 row)

SELECT array_append(ARRAY[1, 2], NULL); -- this might have been meant

array_append

--------------

{1,2,NULL}

</programlisting>

In the examples above, the parser sees an integer array on one side of the

concatenation operator, and a constant of undetermined type on the other.

The heuristic it uses to resolve the constant's type is to assume it's of

the same type as the operator's other input &mdash; in this case,

integer array. So the concatenation operator is presumed to

represent <function>array_cat</>, not <function>array_append</>. When

that's the wrong choice, it could be fixed by casting the constant to the

array's element type; but explicit use of <function>array_append</> might

be a preferable solution.

</para>

</sect2>

<sect2 id="arrays-searching">