?????????????????????SQL??????????????????????????????????
????????????????
????1??NOT IN??????
?????????????в?????????????????????????????
???????????????NOT EXISTS ????????
????2??IS NULL ??IS NOT NULL???????ж???????????
?????ж????????????????????????????????????????????????
????????????????????????????????????棬?磺a is not null ??? a>0 ??a>’’??????????????????????????????????????????????β????????????????
????3??> ?? < ?????????????С?????????
?????????С??????????????????????????????????????????????????????е??????????????????????????????100?????????????????A??30??????A=0??30??????A=1??39??????A=2??1??????A=3????????A>2??A>=3??Ч???к?????????????A>2?ORACLE????????2????????????б?????A>=3?ORACLE????????=3??????????
????4??LIKE??????
????LIKE??????????????????????????????????????????????????????????????ò??????????????????????LIKE ‘%5400%’ ??????????????????????LIKE ‘X5400%’??????÷?Χ??????
?????????????????YW_YHJBQK?????????????????????????????? YY_BH LIKE ‘%5400%’ ?????????????????裬??????YY_BH LIKE ’X5400%’ OR YY_BH LIKE ’B5400%’ ???????YY_BH????????????????Χ???????????????????
????5??UNION??????
????UNION????б????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????UNION???磺
????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