SELECT
  ID
  , NOTE
  , LEFT(NOTE, 20) AS LEFT_TRIM
  , CAST(NOTE AS VARCHAR(20)) AS CAST_TRIM
FROM REFBOOK_DATA_COMMON

Arithmetic overflow or division by zero has occurred.
arithmetic exception, numeric overflow, or string truncation.
string right truncation.
expected length 20, actual 44.
-------------------------------------------------------------
SQLCODE: -802
SQLSTATE: 22001
GDSCODE: 335544321

CAST(LEFT(NOTE, 20) AS VARCHAR(20))