Informix Error -866: Cannot attach tables that contain serial fields.

Reasons / Common Causes

-866 fires when ALTER FRAGMENT ... ATTACH targets a table containing a SERIAL/SERIAL8/ BIGSERIAL column — per the official guidance, serial fields must be dropped, or the column's type modified, before the attach.

1. A table being attached (or the surviving table) with a SERIAL-family column, per the official guidance — the direct, only cause; serial columns auto-generate values per table, which conflicts with how attach combines tables into fragments of one logical table.
2. A primary-key or ID column declared SERIAL that was never intended to need attaching, only discovered when the attach operation itself failed.

Solutions / Resolution

1. Drop the serial field, per the official guidance, if it's not actually needed as an auto-generated identifier going forward.
2. Or modify the column's type from SERIAL/SERIAL8/BIGSERIAL to the corresponding plain integer type (INTEGER/INT8/BIGINT, per the same mapping used for -670), per the official guidance, if the column's existing values need to be preserved but auto-generation isn't required going forward:

   ALTER TABLE orders_2025 MODIFY (order_id INTEGER);
   

3. Then retry the attach, once the serial field is resolved.

Examples

Modifying a serial column before attaching

ALTER TABLE orders_2025 MODIFY (order_id INTEGER);
ALTER FRAGMENT ON TABLE orders ATTACH orders_2025;

Diagnostic Checks

1. Check both the surviving table and the table(s) being attached for SERIAL/SERIAL8/ BIGSERIAL columns, and resolve each (drop or modify type) before retrying.

Related Errors / Related Topics

• -593 — "Cannot specify default value for SERIAL or SERIAL8 or BIGSERIAL column." A related SERIAL-family restriction, in the DEFAULT clause context rather than ATTACH.
• -782 — "Attached table is fragmented." A related ATTACH restriction, on the attached table's fragmentation status.

Drop the serial column, or convert it to the corresponding plain integer type, before attaching.