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<html>
<head>
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<title>COMMENT</title>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
<a name="sql-comment"></a><div class="titlepage"></div>
<div class="refnamediv">
<h2>Name</h2>
<p>COMMENT — define or change the comment of an object</p>
</div>
<a name="id749348"></a><div class="refsynopsisdiv">
<h2>Synopsis</h2>
<pre class="synopsis">COMMENT ON
{
TABLE <em class="replaceable"><code>object_name</code></em> |
COLUMN <em class="replaceable"><code>table_name</code></em>.<em class="replaceable"><code>column_name</code></em> |
AGGREGATE <em class="replaceable"><code>agg_name</code></em> (<em class="replaceable"><code>agg_type</code></em>) |
CAST (<em class="replaceable"><code>sourcetype</code></em> AS <em class="replaceable"><code>targettype</code></em>) |
CONSTRAINT <em class="replaceable"><code>constraint_name</code></em> ON <em class="replaceable"><code>table_name</code></em> |
CONVERSION <em class="replaceable"><code>object_name</code></em> |
DATABASE <em class="replaceable"><code>object_name</code></em> |
DOMAIN <em class="replaceable"><code>object_name</code></em> |
FUNCTION <em class="replaceable"><code>func_name</code></em> ( [ [ <em class="replaceable"><code>argmode</code></em> ] [ <em class="replaceable"><code>argname</code></em> ] <em class="replaceable"><code>argtype</code></em> [, ...] ] ) |
INDEX <em class="replaceable"><code>object_name</code></em> |
LARGE OBJECT <em class="replaceable"><code>large_object_oid</code></em> |
OPERATOR <em class="replaceable"><code>op</code></em> (<em class="replaceable"><code>leftoperand_type</code></em>, <em class="replaceable"><code>rightoperand_type</code></em>) |
OPERATOR CLASS <em class="replaceable"><code>object_name</code></em> USING <em class="replaceable"><code>index_method</code></em> |
[ PROCEDURAL ] LANGUAGE <em class="replaceable"><code>object_name</code></em> |
RULE <em class="replaceable"><code>rule_name</code></em> ON <em class="replaceable"><code>table_name</code></em> |
SCHEMA <em class="replaceable"><code>object_name</code></em> |
SEQUENCE <em class="replaceable"><code>object_name</code></em> |
TRIGGER <em class="replaceable"><code>trigger_name</code></em> ON <em class="replaceable"><code>table_name</code></em> |
TYPE <em class="replaceable"><code>object_name</code></em> |
VIEW <em class="replaceable"><code>object_name</code></em>
} IS <em class="replaceable"><code>'text'</code></em></pre>
</div>
<div class="refsect1" lang="en">
<a name="id749585"></a><h2>Description</h2>
<p> <code class="command">COMMENT</code> stores a comment about a database object.
</p>
<p> To modify a comment, issue a new <code class="command">COMMENT</code> command for the
same object. Only one comment string is stored for each object.
To remove a comment, write <code class="literal">NULL</code> in place of the text
string.
Comments are automatically dropped when the object is dropped.
</p>
<p> Comments can be
easily retrieved with the <span class="application">psql</span> commands
<code class="command">\dd</code>, <code class="command">\d+</code>, and <code class="command">\l+</code>.
Other user interfaces to retrieve comments can be built atop
the same built-in functions that <span class="application">psql</span> uses, namely
<code class="function">obj_description</code> and <code class="function">col_description</code>
(see <a href="functions-info.html#functions-info-comment-table" title="Table9.43.Comment Information Functions">Table9.43, “Comment Information Functions”</a>).
</p>
</div>
<div class="refsect1" lang="en">
<a name="id749677"></a><h2>Parameters</h2>
<div class="variablelist"><dl>
<dt>
<span xmlns="http://www.w3.org/TR/xhtml1/transitional" class="term"><em xmlns="" class="replaceable"><code>object_name</code></em></span><br xmlns="http://www.w3.org/TR/xhtml1/transitional"></br><span xmlns="http://www.w3.org/TR/xhtml1/transitional" class="term"><em xmlns="" class="replaceable"><code>table_name.column_name</code></em></span><br xmlns="http://www.w3.org/TR/xhtml1/transitional"></br><span xmlns="http://www.w3.org/TR/xhtml1/transitional" class="term"><em xmlns="" class="replaceable"><code>agg_name</code></em></span><br xmlns="http://www.w3.org/TR/xhtml1/transitional"></br><span xmlns="http://www.w3.org/TR/xhtml1/transitional" class="term"><em xmlns="" class="replaceable"><code>constraint_name</code></em></span><br xmlns="http://www.w3.org/TR/xhtml1/transitional"></br><span xmlns="http://www.w3.org/TR/xhtml1/transitional" class="term"><em xmlns="" class="replaceable"><code>func_name</code></em></span><br xmlns="http://www.w3.org/TR/xhtml1/transitional"></br><span xmlns="http://www.w3.org/TR/xhtml1/transitional" class="term"><em xmlns="" class="replaceable"><code>op</code></em></span><br xmlns="http://www.w3.org/TR/xhtml1/transitional"></br><span xmlns="http://www.w3.org/TR/xhtml1/transitional" class="term"><em xmlns="" class="replaceable"><code>rule_name</code></em></span><br xmlns="http://www.w3.org/TR/xhtml1/transitional"></br><span class="term"><em class="replaceable"><code>trigger_name</code></em></span>
</dt>
<dd><p> The name of the object to be commented. Names of tables,
aggregates, domains, functions, indexes, operators, operator classes,
sequences, types, and views may be schema-qualified.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>agg_type</code></em></span></dt>
<dd><p> The argument data type of the aggregate function, or
<code class="literal">*</code> if the function accepts any data type.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>sourcetype</code></em></span></dt>
<dd><p> The name of the source data type of the cast.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>targettype</code></em></span></dt>
<dd><p> The name of the target data type of the cast.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>argmode</code></em></span></dt>
<dd><p> The mode of a function argument: either <code class="literal">IN</code>, <code class="literal">OUT</code>,
or <code class="literal">INOUT</code>. If omitted, the default is <code class="literal">IN</code>.
Note that <code class="command">COMMENT ON FUNCTION</code> does not actually pay
any attention to <code class="literal">OUT</code> arguments, since only the input
arguments are needed to determine the function's identity.
So it is sufficient to list the <code class="literal">IN</code> and <code class="literal">INOUT</code>
arguments.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>argname</code></em></span></dt>
<dd><p> The name of a function argument.
Note that <code class="command">COMMENT ON FUNCTION</code> does not actually pay
any attention to argument names, since only the argument data
types are needed to determine the function's identity.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>argtype</code></em></span></dt>
<dd><p> The data type(s) of the function's arguments (optionally
schema-qualified), if any.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>large_object_oid</code></em></span></dt>
<dd><p> The OID of the large object.
</p></dd>
<dt><span class="term"><code class="literal">PROCEDURAL</code></span></dt>
<dd><p> This is a noise word.
</p></dd>
<dt><span class="term"><em class="replaceable"><code>text</code></em></span></dt>
<dd><p> The new comment, written as a string literal; or <code class="literal">NULL</code>
to drop the comment.
</p></dd>
</dl></div>
</div>
<div class="refsect1" lang="en">
<a name="id749927"></a><h2>Notes</h2>
<p> A comment for a database can only be created in that database,
and will only be visible in that database, not in other databases.
</p>
<p> 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.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id749944"></a><h2>Examples</h2>
<p> Attach a comment to the table <code class="literal">mytable</code>:
</p>
<pre class="programlisting">COMMENT ON TABLE mytable IS 'This is my table.';</pre>
<p>
Remove it again:
</p>
<pre class="programlisting">COMMENT ON TABLE mytable IS NULL;</pre>
<p>
</p>
<p> Some more examples:
</p>
<pre class="programlisting">COMMENT ON AGGREGATE my_aggregate (double precision) IS 'Computes sample variance';
COMMENT ON CAST (text AS int4) IS 'Allow casts from text to int4';
COMMENT ON COLUMN my_table.my_column IS 'Employee ID number';
COMMENT ON CONVERSION my_conv IS 'Conversion to UTF8';
COMMENT ON DATABASE my_database IS 'Development Database';
COMMENT ON DOMAIN my_domain IS 'Email Address Domain';
COMMENT ON FUNCTION my_function (timestamp) IS 'Returns Roman Numeral';
COMMENT ON INDEX my_index IS 'Enforces uniqueness on employee ID';
COMMENT ON LANGUAGE plpython IS 'Python support for stored procedures';
COMMENT ON LARGE OBJECT 346344 IS 'Planning document';
COMMENT ON OPERATOR ^ (text, text) IS 'Performs intersection of two texts';
COMMENT ON OPERATOR - (NONE, text) IS 'This is a prefix operator on text';
COMMENT ON OPERATOR CLASS int4ops USING btree IS '4 byte integer operators for btrees';
COMMENT ON RULE my_rule ON my_table IS 'Logs updates of employee records';
COMMENT ON SCHEMA my_schema IS 'Departmental data';
COMMENT ON SEQUENCE my_sequence IS 'Used to generate primary keys';
COMMENT ON TABLE my_schema.my_table IS 'Employee Information';
COMMENT ON TRIGGER my_trigger ON my_table IS 'Used for RI';
COMMENT ON TYPE complex IS 'Complex number data type';
COMMENT ON VIEW my_view IS 'View of departmental costs';</pre>
<p>
</p>
</div>
<div class="refsect1" lang="en">
<a name="id750003"></a><h2>Compatibility</h2>
<p> There is no <code class="command">COMMENT</code> command in the SQL standard.
</p>
</div>
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