Informix Error -519: Cannot update column to illegal value.

Reasons / Common Causes

-519 fires when an expression in an UPDATE ... SET clause itself evaluates to an error — the column being updated isn't the problem; the expression computing its new value is.

1. A built-in function called with invalid arguments within the SET clause — per the official guidance's explicit examples, LENGTH and DATE are common culprits (e.g. DATE() given a string that isn't a valid date format).
2. An arithmetic expression that overflows or divides by zero as part of computing the new column value.
3. A type-conversion expression given a value it can't actually convert (a string that isn't numeric passed where a numeric conversion is expected).

Solutions / Resolution

1. Check each expression in the SET clause for validity, per the official guidance, working through them one at a time rather than assuming the failure is in the column itself.
2. Look in particular at built-in function calls such as LENGTH and DATE, per the official guidance, checking that the arguments passed are of a type/format the function actually accepts.
3. Isolate the failing expression by testing it in a standalone SELECT before including it in the UPDATE, since a SELECT will surface the same evaluation error more cheaply.

Examples

An invalid DATE() argument

UPDATE orders SET ship_date = DATE('not-a-date') WHERE order_id = 42;
-- -519: DATE() can't parse 'not-a-date'

Isolating the failing expression first

SELECT DATE('not-a-date') FROM systables WHERE tabid = 1;
-- reproduces the same evaluation error, without touching any table's data

Diagnostic Checks

1. Test each SET-clause expression independently via a standalone SELECT to find which one is actually failing before assuming the issue is elsewhere in the statement.
2. Review the argument types/formats expected by any built-in function used, especially LENGTH/DATE, against what's actually being passed.

Related Errors / Related Topics

No closely related error codes are cross-referenced for -519 in this set yet.

The failure is in evaluating an expression in the SET clause, not the target column — isolate the expression with a standalone SELECT to find it quickly.