Function Matching Rules for UDFs - apache/drill GitHub Wiki

Rules of Thumb

Given the type conversion rules, we can get the most bang out of our UDFs if we do the following:

• For simple UDFs, allow Drill to do null handling. (For aggregates, we must do it.) Drill will then pass our function only non-nullable holders.
• Choose the Float8 type (simple) or NullableFloat8 type (aggregates) for arguments as it will work with any of Drill's integral of floating point types (Drill do any necessary conversion.)
• If the argument is best defined as an integer, choose BigInt as it will work for all integral types (including the BigInt type used for JSON integers.)