Informix Error -647: Error evaluating math library function function-name.

Reasons / Common Causes

-647 fires when a math library function (SQRT, LOG, LN, EXP, and similar) is called with a value of the correct type but one that's mathematically invalid for that function — per the official guidance, the data type is fine; the specific value passed isn't appropriate.

1. SQRT() (or another function requiring a non-negative argument) called with a negative value — a classic example of a type-correct but mathematically invalid input.
2. LOG()/LN() called with zero or a negative value, since logarithms aren't defined there.
3. A calculation feeding an out-of-domain intermediate value into a math function, where the invalid value wasn't obvious at the point the function call was written, because it depends on the data.

Solutions / Resolution

1. Check that a legitimate value is being passed to the function, per the official guidance — review the function's mathematical domain (non-negative for SQRT, positive for LOG/LN, etc.) against what the expression can actually produce.
2. Add a guard condition (a CASE expression or a WHERE clause filter) to exclude out-of-domain values before they reach the math function, if the underlying data can legitimately contain them.
3. Trace back through the expression feeding the function call if the invalid value isn't supplied directly as a literal, to find where an out-of-domain value is being produced.

Examples

An out-of-domain argument

SELECT SQRT(balance) FROM accounts;
-- -647: some accounts have a negative balance

Guarding against it

SELECT CASE WHEN balance >= 0 THEN SQRT(balance) ELSE NULL END FROM accounts;

Diagnostic Checks

1. Identify the specific math function named in the error and check its mathematical domain.
2. Query for rows whose computed argument falls outside that domain, to confirm which data is triggering the failure:

   SELECT * FROM accounts WHERE balance < 0;
   

Related Errors / Related Topics

No closely related error codes are cross-referenced for -647 in this set yet.

A domain error, not a type error — check the function's valid input range against what the underlying data can actually produce, and guard against out-of-domain values.