</para>

</sect3>

<sect3>

<sect3 id="datatype-datetime-special-values">

<title>Special Values</title>

<indexterm>

type:

<literal>CURRENT_DATE</literal>, <literal>CURRENT_TIME</literal>,

<literal>CURRENT_TIMESTAMP</literal>, <literal>LOCALTIME</literal>,

<literal>LOCALTIMESTAMP</literal>. The latter four accept an

optional subsecond precision specification. (See <xref

<literal>LOCALTIMESTAMP</literal>. (See <xref

linkend="functions-datetime-current">.) Note that these are

SQL functions and are <emphasis>not</> recognized in data input strings.

</para>

<caution>

<para>

While the input strings <literal>now</literal>,

<literal>today</literal>, <literal>tomorrow</literal>,

and <literal>yesterday</literal> are fine to use in interactive SQL

commands, they can have surprising behavior when the command is

saved to be executed later, for example in prepared statements,

views, and function definitions. The string can be converted to a

specific time value that continues to be used long after it becomes

stale. Use one of the SQL functions instead in such contexts.

For example, <literal>CURRENT_DATE + 1</literal> is safer than

<literal>'tomorrow'::date</literal>.

</para>

</caution>

</sect3>

</sect2>

<programlisting>

SELECT CURRENT_TIMESTAMP;

SELECT now();

SELECT TIMESTAMP 'now'; --incorrect for use with DEFAULT

SELECT TIMESTAMP 'now'; --but see tip below

</programlisting>

</para>

<tip>

<para>

You do not want to use the third form when specifying a <literal>DEFAULT</>

clause while creating a table. The system will convert <literal>now</literal>

Do not use the third form when specifying a value to be evaluated later,

for example in a <literal>DEFAULT</literal> clause for a table column.

The system will convert <literal>now</literal>

to a <type>timestamp</type> as soon as the constant is parsed, so that when

the default value is needed,

the time of the table creation would be used! The first two

forms will not be evaluated until the default value is used,

because they are function calls. Thus they will give the desired

behavior of defaulting to the time of row insertion.

(See also <xref linkend="datatype-datetime-special-values">.)

</para>

</tip>

</sect2>