I am setting a variable value with CONCAT Function. If the value for the column is NULL then I want empty string to be returned and if not null then the date should be returned as per the specified format.

SET COLUMN_SELECTION_STRING = 
CONCAT('IFNULL(TRIM(`MAIN`.''', COLUMN_NAME, '),''),STR_TO_DATE(TRIM(`MAIN`.`', COLUMN_NAME, '`), ''%Y-%m-%d %H:%i:%s'')')

However, I get the following string as a result with character added

IFNULL(TRIM(`MAIN`.'EFFECTIVE_DATE),'),STR_TO_DATE(TRIM(`MAIN`.`EFFECTIVE_DATE`), '%Y-%m-%d %H:%i:%s')

How do I get the string without