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<row>

<entry><function>current_timestamp</function></entry>

<entry><type>timestamp</type></entry>

<entry>date and time; see also <link

<entry>Date and time; see <link

linkend="functions-datetime-current">below</link>

</entry>

<entry></entry>

<entry><function>now</function>()</entry>

<entry><type>timestamp</type></entry>

<entry>Current date and time (equivalent to

<function>current_timestamp</function>); seealso<link

<function>current_timestamp</function>); see <link

linkend="functions-datetime-current">below</link>

</entry>

<entry></entry>

<structfield>usesysid</> value.

</para>

<table>

<title>Comment Information Functions</>

<tgroup cols="3">

<thead>

<row><entry>Name</> <entry>Return Type</> <entry>Description</></row>

</thead>

<tbody>

<row>

<entry><function>obj_description</>(<parameter>objectOID</parameter>, <parameter>tablename</>)</entry>

<entry><type>text</></entry>

<entry>Get comment for a database object</>

</row>

<row>

<entry><function>obj_description</>(<parameter>objectOID</parameter>)</entry>

<entry><type>text</></entry>

<entry>Get comment for a database object (<emphasis>deprecated</>)</entry>

</row>

<row>

<entry><function>col_description</>(<parameter>tableOID</parameter>, <parameter>columnnumber</>)</entry>

<entry><type>text</></entry>

<entry>Get comment for a table column</>

</row>

</tbody>

</tgroup>

</table>

<indexterm zone="functions-misc">

<primary>obj_description</primary>

</indexterm>

<indexterm zone="functions-misc">

<primary>col_description</primary>

</indexterm>

<para>

These functions extract comments previously stored with the

<command>COMMENT</> command. <literal>NULL</> is returned if

no comment can be found matching the specified parameters.

</para>

<para>

The two-parameter form of <function>obj_description()</> returns the

comment for a database object specified by its OID and the name of the

containing system catalog. For example,

<literal>obj_description(123456,'pg_class')</>

would retrieve the comment for a table with OID 123456.

The one-parameter form of <function>obj_description()</> requires only

the object OID. It is now deprecated since there is no guarantee that

OIDs are unique across different system catalogs; therefore, the wrong

comment could be returned.

</para>

<para>

<function>col_description()</> returns the comment for a table column,

which is specified by the OID of its table and its column number.

<function>obj_description()</> cannot be used for table columns since

columns do not have OIDs of their own.

</para>

</sect1>

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Description

</title>

<para>

<command>COMMENT</command> adds a comment to an object that can be

<command>COMMENT</command> stores a comment about a database object.

Comments can be

easily retrieved with <command>psql</command>'s

<command>\dd</command>, <command>\d+</command>, or <command>\l+</command> commands.

To remove a comment, write <literal>NULL</literal>.

<command>\dd</command>, <command>\d+</command>, or <command>\l+</command>

commands. Other user interfaces to retrieve comments can be built atop

the same built-in functions that <command>psql</command> uses, namely

<function>obj_description()</> and <function>col_description()</>.

</para>

<para>

To modify a comment, issue a new <command>COMMENT</> command for the

same object. Only one comment string is stored for each object.

To remove a comment, write <literal>NULL</literal> in place of the text

string.

Comments are automatically dropped when the object is dropped.

</para>

<para>

It should be noted that there is presently no security mechanism

for comments: any user connected to a database can see all the comments

for objects in that database (although only superusers can change

comments for objects that they don't own). Therefore, don't put

security-critical information in comments.

</para>

</refsect1>

<refsect1 id="R1-SQL-COMMENT-2">