<note>

<para>

The SQL standard requires constraint names to be unique within a

schema; <productname>PostgreSQL</productname>, however, does not

enforce this restriction. If duplicate-named constraints are

stored in the same <productname>PostgreSQL</productname> schema,

a standard-compliant query that expects to return one matching

constraint row might return several, one row for each matching

constraint stored in the specified schema.

When querying the database for constraint information, it is possible

for a standard-compliant query that expects to return one row to

return several. This is because the SQL standard requires constraint

names to be unique within a schema, but

<productname>PostgreSQL</productname> does not enforce this

restriction. <productname>PostgreSQL</productname>

automatically-generated constraint names avoid duplicates in the

same schema, but users can specify such duplicate names.

</para>

</note>