一個SQL語句的優化(sqlserver)
阿新 • • 發佈:2018-08-04
性能 HERE lse union ont sele cit The 原因
最早的寫法:
WITH T AS (SELECT case when Col1 IS NULL OR Col1=N‘‘ then Col2 else Col1 end as Code,case when Col1 IS NULL OR Col1=N‘‘ then 1 else 0 end as Flag FROM YM WHERE Col_076 BETWEEN ‘2018-07-25‘ AND ‘2018-08-03‘ AND Col_478=N‘xx‘ AND Col_346 LIKE N‘%dd%‘), D AS (SELECT Code,province,city FROM Adds)SELECT province AS 省,city as 市,COUNT(1) 票數 FROM (SELECT A.DR_250 as province,A.DR_251 as city FROM T INNER JOIN TB AS A ON A.DR_203=T.Code WHERE T.Flag=0 UNION ALL SELECT D.province,D.city FROM T INNER JOIN D ON D.Code=T.Code WHERE T.Flag=1 UNION ALL SELECT ‘‘ AS province,‘‘ AS city FROM T WHERECode IS NULL OR Code=N‘‘) AS S GROUP BY province,city;
最新的寫法:
SELECT case when Col1 IS NULL OR Col1=N‘‘ then Col2 else Col1 end as Code,case when Col1 IS NULL OR Col1=N‘‘ then 1 else 0 end as Flag into #T FROM YM WHERE Col_076 BETWEEN ‘2018-07-25‘ AND ‘2018-08-03‘ AND Col_478=N‘xx‘ AND Col_346 LIKEN‘%dd%‘; SELECT Code,province,city into #D FROM Adds; SELECT province AS 省,city as 市,COUNT(1) 票數 FROM (SELECT A.DR_250 as province,A.DR_251 as city FROM #T INNER JOIN TB AS A ON A.DR_203=#T.Code WHERE #T.Flag=0 UNION ALL SELECT #D.province,#D.city FROM #T INNER JOIN #D ON #D.Code=#T.Code WHERE #T.Flag=1 UNION ALL SELECT ‘‘ AS province,‘‘ AS city FROM #T WHERE Code IS NULL OR Code=N‘‘) AS S GROUP BY province,city; DROP table #T; DROP table #D;
新的寫法比原始寫法性能高出太多(原語句執行會超時),最大的原因是對with語句理解有誤!!!
一個SQL語句的優化(sqlserver)