/* 找不到 */
SELECT * FROM news WHERE class = NULL
/* 找不到 */
SELECT * FROM news WHERE class IN ( 0 , 1 , NULL )
/* 要這樣寫 */
SELECT * FROM news WHERE class IS NULL
/* 找不到 */
SELECT * FROM news WHERE class = NULL
/* 找不到 */
SELECT * FROM news WHERE class IN ( 0 , 1 , NULL )
/* 要這樣寫 */
SELECT * FROM news WHERE class IS NULL