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Informix Error -577

-577 A constraint of the same type already exists on the column set.

You have placed a constraint (either UNIQUE, PRIMARY KEY, FOREIGN KEY, or CHECK) on a set of columns, but a constraint of the same type on those columns already exists. In the case of a FOREIGN KEY, this error only occurs if the same foreign-key set of columns references the same existing parent key set of columns. Either the constraint was established when the table was created, or it was added later. Because the constraint already exists, it is not added again.

Oninit® Troubleshooting Guidance

Reasons / Common Causes

-577 fires when adding a constraint of a given type (UNIQUE, PRIMARY KEY, FOREIGN KEY, or CHECK) on a column set that already has a constraint of that exact type — per the official guidance, for FOREIGN KEY specifically, this only fires when the same child column set already references the same parent column set, not merely any two foreign keys sharing a child column.

  1. A duplicate UNIQUE/CHECK constraint added to the same column set, whether by direct DDL or as an implicit constraint from a second CREATE INDEX-equivalent operation.
  2. A second PRIMARY KEY attempted on a table that already has one — a table can only have one primary key, so this is a specific case of the general duplicate-constraint-type rule.
  3. A migration/DDL script re-run without checking whether the constraint was already applied, attempting to add the same constraint a second time.
Solutions / Resolution
  1. Recognize that the constraint already exists and doesn't need to be added again, per the official guidance — this is often not an error to fix so much as a no-op to skip.
  2. Confirm the existing constraint's definition matches what was intended, before assuming no action is needed:
    SELECT constrname, constrtype FROM sysconstraints
WHERE tabid = (SELECT tabid FROM systables WHERE tabname = 'orders');
  3. If a genuinely different constraint was intended (different columns, or a different constraint type), correct the DDL rather than assuming the existing one is sufficient.
Examples
Attempting a duplicate constraint
CREATE TABLE orders (order_id INT UNIQUE, status CHAR(10));
ALTER TABLE orders ADD CONSTRAINT UNIQUE (order_id) CONSTRAINT uq_orders_id;
-- -577: order_id already has a UNIQUE constraint
Checking existing constraints first
SELECT constrname, constrtype FROM sysconstraints
WHERE tabid = (SELECT tabid FROM systables WHERE tabname = 'orders');
Diagnostic Checks
  1. Query sysconstraints for existing constraints on the table before attempting to add a new one, to confirm whether the intended constraint (type and column set) is already present.
Related Errors / Related Topics
  • -540 — "Write failed on constraints." A related constraint-DDL error, about a naming collision or ISAM-level failure during the write rather than the constraint already existing.

Often not an error to fix, but a signal the constraint is already there — query sysconstraints to confirm before assuming further action is needed.