Informix Error -856

Reasons / Common Causes

-856 fires when an attempt to add a ROWID column to a table targets one that already has one — per the official guidance, a table can't have ROWID created for it more than once.

1. ALTER TABLE ... ADD ROWIDS (or equivalent) attempted on a table that already has a ROWID column, per the official guidance — the direct, only cause.
2. A migration/deployment script re-run without checking the table's current ROWID status.

Solutions / Resolution

1. Change the SQL statement, per the official guidance — since the table already has ROWID, no action is needed, or the statement should be removed from the script/migration.
2. Check the table's current ROWID status before attempting to add one:

   SELECT tabname FROM systables WHERE tabname = 'orders';
   -- check whether the table currently has a rowid column via the
   -- appropriate fragmentation/rowid catalog detail for the server version
   -- in use, or simply query ROWID directly:
   SELECT ROWID FROM orders WHERE 1 = 0;
   -- succeeds only if the table currently has a ROWID column
   

Examples

Checking ROWID status before attempting to add it

SELECT ROWID FROM orders WHERE 1 = 0;
-- if this succeeds, orders already has ROWID -- don't attempt to add it again

Diagnostic Checks

1. Confirm whether the table already has a ROWID column before attempting to add one.

Related Errors / Related Topics

• -855 — "Cannot drop rowids on a non-fragmented table." A related ROWID-management restriction, about dropping rather than adding.
• -857 — "Rowids do not exist on table." The mirror-image situation: attempting to drop a ROWID that doesn't currently exist.

The table already has a ROWID column — no action needed, or remove the redundant statement from the script.