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Oracle optimization Efficiency

Source: Internet
Author: User
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1, RowNum

(1)

more slowlySELECTYWLSDM, QYBM, SPZT, CZSJ, CZRYDM fromGH_HSWHEREYwlsdminch(SELECTYwlsdm fromGh_hsWHERESpzt= '2')
More quicklySELECTYWLSDM, QYBM, SPZT, CZSJ, CZRYDM fromGH_HSWHEREYwlsdminch(SELECTYwlsdm fromGh_hsWHERESpzt= '2'  andRowNum<=(SELECT COUNT(*) fromGH_HS HSWHERE EXISTS(SELECTYwlsdm fromGh_hsWHERESpzt= '2')))

2, with as temporary table

Select *  from ( withQYBM as (SelectGX.QYBM from(SelectA.GHDM fromGH_GHDM a start withA.ghdm= '1'Connect byPrior A.GHDM=a.sjghdm) GHInner JoinGH_QYGHGX GX onGh.ghdm=gx.tjghdm), YG as (   Select *  fromGh_jc_yg TwhereT.yglx= '0')SelectYg.*  fromQYBM, YGwhereQybm.qybm=YG.QYGHDM)

Oracle optimization Efficiency

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