今天开发问我，为什么!=操作不能获取值为null记录：
abce=# select id, abce-# a_no, abce-# a_code, abce-# a_number, abce-# date_receive, abce-# bank_a, abce-# status abce-# from abce-# erp_a_examine abce-# where abce-# ( a_number = '1023' and a_code = '231174' and status != '已作废' ); id | a_no | a_code | a_number | date_receive | bank_a | status -----+------+--------+----------+--------------+--------+-------- (0 rows) abce=# select id, abce-# a_no, abce-# a_code, abce-# a_number, abce-# date_receive, abce-# bank_a, abce-# status abce-# from abce-# erp_a_examine abce-# where abce-# ( a_number = '1023' and a_code = '231174' ); id | a_no | a_code | a_number | date_receive | bank_a | status -----+------+--------+----------+--------------+--------+-------- 333 | 1023 | 231174 | 12155 | 2010-03-02 | | (1 row) abce=#
只是因为null是非safe的操作。
