Informix Error -946: Source string for UPPER, LOWER, and INITCAP must be of string type.

Reasons / Common Causes

-946 fires when UPPER, LOWER, or INITCAP is called with an argument that isn't a character type — per the official guidance, the input must be a string type.

1. A non-string value passed to UPPER/LOWER/INITCAP, per the official guidance — a numeric or date value where a character string is required.
2. A column/expression of the wrong type referenced by mistake, where a similarly-named string column was intended instead.

Solutions / Resolution

1. Confirm the source argument is character-typed, per the official guidance.
2. Cast explicitly if a conversion is genuinely needed:

   SELECT UPPER(order_id::VARCHAR(10)) FROM orders;
   

Examples

The disallowed non-string argument

SELECT UPPER(order_id) FROM orders;
-- -946: order_id is INT, not a string type

Corrected — explicit cast

SELECT UPPER(order_id::VARCHAR(10)) FROM orders;

Diagnostic Checks

1. Check the declared type of the argument passed to UPPER/LOWER/INITCAP against the string-type requirement.

Related Errors / Related Topics

• -941 — "String processing error while evaluating function (function_name)." A related case-conversion-function error, about an invalid character within an otherwise-valid string argument, rather than a non-string argument type entirely.
• -880 — "Trim character and trim source must be of string data type." The same string-type requirement, for TRIM's arguments rather than UPPER/LOWER/INITCAP.

The same string-type requirement as -880, here for UPPER/LOWER/INITCAP — cast explicitly if the source is a non-string type.