Informix Error -2956: You may not set display field field-tag to a value because none of its associated database columns belong to the same table as table, nor is it a variable display-only field.

Reasons / Common Causes

-2956 fires when a LET statement assigns a value to a field whose associated columns don't belong to a table named in the control block's opening command, and the field isn't a display-only variable either — per the official guidance, values cannot be assigned across tables in a LET statement.

1. A LET target field whose associated columns belong to a different table than the ones named in the control block's opening command, per the official guidance — the direct cause.
2. The target field is not a display-only field, per the official guidance — the exception that would otherwise permit the assignment.

Solutions / Resolution

1. Confirm every column associated with the LET target field belongs to a table named in the control block's opening command, per the official guidance.
2. Alternatively, make the field a display-only field, per the official guidance, if it doesn't need to be tied to a table column.

Examples

A LET target belonging to the wrong table

AFTER UPDATE OF orders
  LET customer.name = "Unknown";
-- -2956: customer.name isn't in the orders table named in this block

Corrected

AFTER UPDATE OF orders
  LET status = "Reviewed";
-- status is DISPLAYONLY, so no table membership is required

Diagnostic Checks

1. Check the table membership of every column associated with a LET target field, and confirm it matches the enclosing control block's table, or mark the field DISPLAYONLY.

Related Errors / Related Topics

• -2944 — "You may apply the after add, update, query, or remove commands to a table only -- not a column." A related control-block-scoping error, about the block's own opening command rather than a LET target inside it.
• -2945 — official title text duplicated from -2944 on the live site, but its actual description covers the same aggregate/table-membership scoping rule that -2956 applies to LET assignments.

A LET statement assigns to a field whose columns aren't in the control block's table, and the field isn't display-only — align the table or mark it DISPLAYONLY.