Informix Error -9844: Invalid function function_name used in a functional key.

Reasons / Common Causes

-9844 fires when a function used as a CREATE INDEX functional key part isn't allowed there — per the official guidance.

1. A variant function used as a functional key part, per the official guidance — the direct, only named cause.

Solutions / Resolution

1. Make sure the function used isn't a variant function, per the official guidance — use a function created with NOT VARIANT.

Examples

A variant function used in a functional key

CREATE INDEX idx1 ON tab(my_variant_func(col));   -- -9844

Corrected

CREATE FUNCTION my_func(a INT) RETURNING INT NOT VARIANT ...;
CREATE INDEX idx1 ON tab(my_func(col));

Diagnostic Checks

1. Check whether the function used in the functional key is variant or not variant, and switch to a NOT VARIANT function if needed.

Related Errors / Related Topics

• -9843 — "Invalid number of arguments for functional key." A related functional-key validity error, on argument count rather than the function being variant.
• -9848 — "Functional key part cannot use a variant function function_name." The same restriction, stated more explicitly for variant functions.

An invalid (variant) function was used as a functional key part — use a NOT VARIANT function instead.