发现SQL 2000一个缺陷

SELECT TCID FROM
(SELECT fd_testcase_id AS TCID, t_testitem.fd_testcase_num AS NUM
FROM t_testcase LEFT JOIN t_testitem ON
t_testcase.fd_num = t_testitem.fd_testcase_num
WHERE t_testcase.fd_function_id LIKE ‘%FDA-U:1.30.R%’ A
ND t_testcase.fd_needlevel NOT LIKE ‘%备用%’
AND t_testcase.fd_num = NULL AND t_testcase.fd_project_id=214) T WHERE NUM IS NULL

和

SELECT fd_testcase_id AS TCID, t_testitem.fd_testcase_num
FROM t_testcase LEFT JOIN t_testitem ON
t_testcase.fd_num = t_testitem.fd_testcase_num
WHERE t_testcase.fd_function_id LIKE ‘%FDA-U:1.30.R%’
AND t_testcase.fd_needlevel NOT LIKE ‘%备用%’
AND (t_testcase.fd_num IS NULL)
AND t_testcase.fd_project_id=214

执行的结果竟然不同！