IBM Db2 Sql 查询优化

Question

我有这个查询：

select DBSAITE.MITEM, DBSAITE.MPDSC, DBSAITE.MUTMS, MVSACPE.COSTUN,  PCSACST.CSTTYAPP, 
SUM(PCSACST.CSTBURD1 + PCSACST.CSTBURD2 + PCSACST.CSTLABOR + 
PCSACST.CSTMAT + PCSACST.CSTSETUP + PCSACST.CSTEXTRN) as COSTO_STD 
from MVSACPE, PCSACST, DBSAITE
WHERE PCSACST.CSTCOSC = MVSACPE.CODSOC
AND PCSACST.CSTITEM = MVSACPE.CODITM
AND MVSACPE.CODITM = DBSAITE.MITEM
AND DBSAITE.MCOSC = 'GRS'
AND MVSACPE.CODSOC = 'GRS23'
AND MVSACPE.DTPERI = '201512'
AND MVSACPE.CODMAG = 'ALL'
AND MVSACPE.CODCOS = 'MPR' 
AND PCSACST.CSTDATE = '20150630'
AND PCSACST.CSTTYPE = 'SG'
GROUP BY DBSAITE.MITEM, DBSAITE.MPDSC, DBSAITE.MUTMS, MVSACPE.COSTUN,PCSACST.CSTTYAPP

我想以某种方式优化查询，因为连接处理数十万条记录并且非常慢（3 分钟）。

有什么建议吗？

Answer 1

首先，使用显式 JOIN 语法重写查询。如果不出意外，这会让您更容易看到要做什么：

select DBSAITE.MITEM, DBSAITE.MPDSC, DBSAITE.MUTMS, MVSACPE.COSTUN,  PCSACST.CSTTYAPP, 
SUM(PCSACST.CSTBURD1 + PCSACST.CSTBURD2 + PCSACST.CSTLABOR + 
PCSACST.CSTMAT + PCSACST.CSTSETUP + PCSACST.CSTEXTRN) as COSTO_STD 
from MVSACPE JOIN
     PCSACST
     ON PCSACST.CSTCOSC = MVSACPE.CODSOC AND
        PCSACST.CSTITEM = MVSACPE.CODITM JOIN
     DBSAITE
     ON MVSACPE.CODITM = DBSAITE.MITEM
WHERE DBSAITE.MCOSC = 'GRS' AND
      MVSACPE.CODSOC = 'GRS23' AND
      MVSACPE.DTPERI = '201512' AND
      MVSACPE.CODMAG = 'ALL' AND
      MVSACPE.CODCOS = 'MPR' AND
      PCSACST.CSTDATE = '20150630' AND
      PCSACST.CSTTYPE = 'SG'
GROUP BY DBSAITE.MITEM, DBSAITE.MPDSC, DBSAITE.MUTMS, MVSACPE.COSTUN,PCSACST.CSTTYAPP;

索引可能有助于查询。目前尚不清楚哪些条件最具选择性。缺乏其他信息，一个好的起点是这些：

- `MVSACPE(CODSOC, DTPERI, CODMAG, CODCOS, CODITM)`
- `PCSACST(CSTCOSC, CSTITEM, CSTDATE, CSTTYPE)`
- `DBSAITE(MITEM, MCOSC)`

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