Informix Error -326

Reasons / Common Causes

-326 is an implementation limit on composite foreign keys: a referential constraint can list at most 16 columns on standard Informix, or 8 columns on IBM Informix SE — a much narrower ceiling on the older SE engine.

1. A composite foreign key referencing more columns than the server's limit — the direct cause, most likely to surface on wide, highly composite keys.
2. Running the same schema against both standard Informix and Informix SE, where a constraint valid on one (up to 16 columns) exceeds the other's stricter 8-column limit.
3. A key design that grew over time — columns added to a composite key incrementally without revisiting whether the total was approaching either limit.

Solutions / Resolution

1. Reduce the number of columns in the referential constraint to within the applicable limit (16 for standard Informix, 8 for Informix SE), per the official guidance.
2. Consider introducing a surrogate key (a single-column synthetic identifier) instead of a wide composite key, if the natural key genuinely needs more columns than the limit allows.
3. If targeting Informix SE specifically, design composite keys with the stricter 8-column limit in mind from the start, even if the primary target is standard Informix.

Examples

A composite key exceeding the limit

-- Assume this composite key spans 17 columns on standard Informix
ALTER TABLE order_line_items ADD CONSTRAINT
    FOREIGN KEY (col1, col2, col3, /* ... 17 columns total ... */)
    REFERENCES order_headers(col1, col2, col3, /* ... */);
-- -326: exceeds the 16-column limit

Fix — introduce a surrogate key to replace the wide composite:

ALTER TABLE order_headers ADD (order_header_id SERIAL);
ALTER TABLE order_headers ADD CONSTRAINT PRIMARY KEY (order_header_id);

ALTER TABLE order_line_items ADD (order_header_id INTEGER);
ALTER TABLE order_line_items ADD CONSTRAINT
    FOREIGN KEY (order_header_id) REFERENCES order_headers(order_header_id);

Diagnostic Checks

1. Count the columns in the referential constraint's column list and compare against the applicable limit for the target server edition.
2. Confirm which Informix edition (standard vs. SE) the schema is being deployed against, since the limit differs significantly between them.

Related Errors / Related Topics

• -295 — "Referenced and referencing tables have to be in the same database." Another referential-constraint restriction in the same general foreign-key-setup family.
• -297 — "Cannot find unique constraint or primary key on referenced table table-name." Another constraint-setup error in the same family.

A surrogate single-column key is usually a cleaner fix than trimming a genuinely wide natural composite key down to fit the column limit.