Informix Error -540

Reasons / Common Causes

-540 fires while the server is writing a new constraint's catalog entries, most often because the constraint's name collides with an existing name in the same namespace.

1. A constraint name duplicating another constraint, table, or index name — per the official guidance, the most likely cause, since Informix requires these names to be unique within their scope.
2. An underlying ISAM-level failure during the catalog write — per the official guidance, check the accompanying ISAM error code when a naming collision isn't the explanation.
3. A system-generated constraint name colliding with a name chosen explicitly elsewhere, since unnamed constraints get an automatically generated name that could theoretically collide with one a later statement names explicitly.

Solutions / Resolution

1. Check whether the constraint's name duplicates an existing constraint, table, or index name, per the official guidance — query sysconstraints/systables/sysindexes for the name before retrying.
2. Repeat the statement with a unique name, per the official guidance, once a collision is confirmed.
3. If no naming collision is found, check the accompanying ISAM error code, per the official guidance, for the actual underlying cause.

Examples

A duplicate constraint name

ALTER TABLE orders ADD CONSTRAINT
  CHECK (status IN ('pending','shipped')) CONSTRAINT ck_status;
-- ck_status already exists as a constraint on a different table
-- -540: Write failed on constraints.

Checking for the collision

SELECT constrname, tabid FROM sysconstraints WHERE constrname = 'ck_status';

Corrected with a unique name

ALTER TABLE orders ADD CONSTRAINT
  CHECK (status IN ('pending','shipped')) CONSTRAINT ck_orders_status;

Diagnostic Checks

1. Query sysconstraints, systables, and sysindexes for the chosen constraint name to confirm whether it collides with an existing object before assuming an ISAM-level cause.
2. Check the accompanying ISAM error code if no naming collision is found.

Related Errors / Related Topics

No closely related error codes are cross-referenced for -540 in this set yet.

Usually a name collision — check sysconstraints/systables/sysindexes for the chosen name first, then fall back to the accompanying ISAM error code.