A.SELECT B.FROM C.ORDER BY D.WHERE
A.Where em_id=‘11%’ B.Where em_id AS ‘11%’ C.Where em_id like ‘11%’ D.Where em_id link ‘11%’
A.SELECT * FROM sc WHERE grade=NULL B.SELECT * FROM sc WHERE grade IS “ ” C.SELECT * FROM sc WHERE grade=‘ ’ D.SELECT * FROM sc WHERE grade IS NULL