SQL查询条件中操作符暗含该字段不为空

--公文提醒列表的SQL

select a.GW_ID,
a.CMPY_ID,
a.DEPT_ID,
a.DEPT_TOP_ID,
a.DEPT_NAME,
a.DEPT_TOP_NAME,
a.USER_ID,
a.GW_BEGIN_TIME,
a.GW_END_TIME,
a.TMPL_TYPE_CODE,
a.TMPL_ID,
a.GW_TYPE,
a.GW_STATUS,
a.GW_TITLE,
a.GW_TOPIC,
a.GW_PAGE,
a.GW_MEMO,
a.GW_SECRET,
a.GW_EMERGENCY,
a.GW_MAIN_TO,
a.GW_COPY_TO,
a.GW_COPYUP_TO,
a.GW_COSIGN_TO,
a.GW_SEND_TO,
a.GW_PRINT_TO,
a.GW_YEAR,
a.GW_YEAR_NUMBER,
a.GW_YEAR_CODE,
a.GW_FILE_TYPE,
a.GW_FILE_HEAD,
a.GW_FILE_END,
a.GW_SAVE_PERIOD,
a.GW_COPIES,
a.GW_CONTACT_ID,
a.GW_CONTACT_NAME,
a.GW_CONTACT_PHONE,
a.GW_CW_DEPT_ID,
a.GW_CW_DEPT_NAME,
a.GW_CW_DATE,
a.GW_SIGN_DATE,
a.PRINT_STRING,
a.DEL_FLAG,
a.FIELD,
a.USER_NAME,
a.WF_ACT_ID,
a.MIND_CONTENT,
a.GW_FROM_CODE,
a.GW_REG_NUMBER,
a.GW_CODE,
a.GW_CODE_TIME,
a.GW_SIGN_NAME,
a.MIND_CODE,
a.GW_DO_VIEW,
a.GW_SECRET_PERIOD,
a.NEED_ARCH,
a.ARCHIVES_DATE,
a.BOX_NUM,
a.SHUSHENG_PRINT_COPIES,
a.GW_IS_DEPLOYED,
a.GW_YEAR_CODE_CAN_DUP,
a.GW_QUERY_FIELD,
a.GW_END_USER_ID,
a.GW_END_USER_NAME,
a.GW_END_DEPT_ID,
a.GW_END_DEPT_NAME,
a.GW_END_DEPT_TOP_ID,
a.GW_END_DEPT_TOP_NAME,
a.GW_SHOUWEN_BL_TYPE,
a.GW_ARCHIVES_FLAG
from TBL_MSV_GONGWEN a
where CMPY_ID = 3055
and GW_STATUS <> 1
-- (1) and (GW_FILE_END <> ' 123' or GW_FILE_END ='123 ' or GW_FILE_END IS NULL)--办理期限不等于空的
-- (2) and GW_FILE_END <> '123 '
-- and GW_FILE_END is not null
order by GW_FILE_END desc;

解释：

（1）只有这三个条件或运算才组成全集，与不加入这个条件一样。

（2）<> 或 = 等操作符都暗示了左边的字段不为null，GW_FILE_END <> ' 123'相当于（GW_FILE_END <> '123 ' and GW_FILE_END is not null）