raghunandanbhat bff9b1e472 MDEV-36851: COALESCE() returns nullable column while IFNULL() does not ...

Nullability is decided in two stages-

1. Based on argument NULL-ness

Problem:
- COALESCE currently uses a generic logic- "Result of a function
  is nullable if any of the arguments is nullable", which is wrong.
- IFNULL sets nullability using second argument alone, which incorrectly
  sets the result to NULL even when first argument is not null.

Fix:
- Result of COALESCE and IFNULL is set to NULL only if all arguments are
  NULL.

2. Based on type conversion safety of fallback value

Problem:
- The generic `Item_hybrid_func_fix_attributes` logic would mark the
  function's result as nullable if any argument involved a type
  conversion that could yield NULL.

Fix:
- For COALESCE and IFNULL, nullability is set to NOT NULL if the first
  non-null argument can be safely converted to function's target return
  type.
- For other functions, if any argument's conversion to target type could
  result in NULL, the function is marked nullable.

Tests included in `mysql-test/main/func_hybrid_type.test`

2025-06-12 16:58:52 +05:30

..

mysql-test/type_test

MDEV-36851: COALESCE() returns nullable column while IFNULL() does not

2025-06-12 16:58:52 +05:30

CMakeLists.txt

Data type plugins - minor fixes

2019-10-31 11:19:35 +01:00

plugin.cc

cleanup: remove Type_collection::handler_by_name()

2023-07-04 16:37:29 +02:00