?????????????????????SQL??????????????????????????????????
????????????????
????1??NOT IN??????
?????????????胁?????????????????????????????
???????????????NOT EXISTS ????????
????2??IS NULL ??IS NOT NULL???????卸???????????
?????卸????????????????????????????????????????????????
????????????????????????????????????妫�?纾篴 is not null ??? a>0 ??a>’’??????????????????????????????????????????????尾????????????????
????3??> ?? < ?????????????小?????????
?????????小??????????????????????????????????????????????????????械??????????????????????????????100?????????????????A??30??????A=0??30??????A=1??39??????A=2??1??????A=3????????A>2??A>=3??效???泻?????????????A>2?ORACLE????????2????????????斜?????A>=3?ORACLE????????=3??????????
????4??LIKE??????
????LIKE??????????????????????????????????????????????????????????????貌??????????????????????LIKE ‘%5400%’ ??????????????????????LIKE ‘X5400%’??????梅?围??????
?????????????????YW_YHJBQK?????????????????????????????? YY_BH LIKE ‘%5400%’ ?????????????????瑁�??????YY_BH LIKE ’X5400%’ OR YY_BH LIKE ’B5400%’ ???????YY_BH????????????????围???????????????????
????5??UNION??????
????UNION????斜????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????UNION???纾�
????select * from gc_dfys
????union
????select * from ls_jg_dfys
???????SQL????????????????????????????????????????????????????????????????????????????????????????????????
?????????????????UNION ALL?????????UNION?????UNION ALL??????????????????????????
????select * from gc_dfys
????union all
????select * from ls_jg_dfys