????7??where???????????????ú????????????????

???????仰???WHERE?????????????????????????????????????????????????????????ú??????????????????????????????????????????4?????

?4.??Where????ò??????????????μ?????????

?????????????Щ????????????????ò???????????????????????????????????????????Where????????????????????5?????

?5.????????????????????

????8???????t?????????????磨from x??y??z??

???????????Ч????μ???????????????????????????????????????????????????????????е??????????????????Loop join??merge Join??Hash Join?е????????????Ч????μ?????????

????>   ?????????????????????“????”???￡??????????????????????м???????????????????д??where?????????????????????????????????where???????????????????????????м?????????????

????????????????Inner join???????from x??y??z????????