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Postgres documentation

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<para>

To add a check constraint to a table:

<programlisting>

ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5)

ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);

</programlisting>

</para>

<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;

</programlisting>

</para>

<para>

To add a foreign key constraint to a table:

<programlisting>

ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses(address) MATCH FULL

ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses(address) MATCH FULL;

</programlisting>

</para>

<para>

To add a (multi-column) unique constraint to a table:

<programlisting>

ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode)

ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);

</programlisting>

</para>

</refsect1>