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Postgres documentation

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adds a new constraint to the table using the same syntax as <xref

linkend="SQL-CREATETABLE">.

The DROP CONSTRAINT <replaceable class="PARAMETER">constraint</replaceable> clause

drops allCHECKconstraints on the table (and its children) that match <replaceable class="PARAMETER">constraint</replaceable>.

drops all constraints on the table (and its children) that match <replaceable class="PARAMETER">constraint</replaceable>.

The OWNER clause changes the owner of the table to the user <replaceable class="PARAMETER">

new user</replaceable>.

</para>

new default value, using <xref linkend="sql-update">.)

</para>

<para>

Currently only CHECK constraints can be dropped from a table. The RESTRICT

keyword is required, although dependencies are not checked. The CASCADE

option is unsupported. To remove a PRIMARY or UNIQUE constraint, drop the

relevant index using the <xref linkend="SQL-DROPINDEX"> command.

<para>

In DROP CONSTRAINT, the RESTRICT keyword is required, although

dependencies are not yet checked. The CASCADE option is unsupported.

Currently DROP CONSTRAINT drops only CHECK constraints.

To remove a PRIMARY or UNIQUE constraint, drop the

relevant index using the <xref linkend="SQL-DROPINDEX"> command.

To remove FOREIGN KEY constraints you need to recreate

and reload the table, using other parameters to the

<xref linkend="SQL-CREATETABLE">

command.

<xref linkend="SQL-CREATETABLE"> command.

</para>

<para>

For example, to drop all constraints on a table <literal>distributors</literal>:

<para>

To remove a check constraint from a table and all its children:

<programlisting>

ALTER TABLE distributors DROP CONSTRAINT zipchk;

ALTER TABLE distributors DROP CONSTRAINT zipchk RESTRICT;

</programlisting>

</para>