hints的push_pred應用

在項目中優化了一條SQL，當時從40多秒減少到了2秒，感覺很有成就感，現在反過頭來又看了一次，覺得仍然有優化的余地，SQL如下

Sql代碼

SELECT DISTINCT A.CURTITLE AS CTITLE,

A.DMODIFYDATE,

A.NDOCID AS NDOCID,

A.NPROCID AS NPROCID,

B.CPROCNAME AS CPROCNAME,

B.NDAYS AS TRUE_DAYS,

(SYSDATE – A.DMODIFYDATE) AS DAYSLEFT,

A.NDOCSORTID AS NDOCSORTID,

A.NPROCSTATUS AS NPROCSTATUS,

C.CNAME AS DOCSORTNAME,

NVL(D.NJJCD, 0) NJJCD,

D.CDOCFROM AS CDOCFROM,

D.CDOCPRIORITY AS CDOCPRIORITY,

D.CWENHAO,

A.NFWQBOPT,

D.DW

FROM WF_DOC_GW A,

WF_PROCNAME B,

WF_DOCSORT C,

(SELECT ? NVL(CFWZH, ”) AS CWENHAO,

NVL(CFWDW, ‘ ‘) AS DW,

NDOCID,

NJJCD,

NVL(CDOCFROM, ‘ ‘) AS CDOCFROM,

NVL(CDOCPRIORITY, 0) AS CDOCPRIORITY

FROM WF_DOC_GW_SHOUWEN SW

UNION ALL

SELECT NVL(CWENHAO, ‘ ‘) AS CWENHAO,

NVL(CFWDW, ”) AS DW,

NDOCID,

NJJCD,

NVL(CDOCFROM, ‘本單位發文’) AS CDOCFROM,

NVL(CDOCPRIORITY, 0) AS CDOCPRIORITY

FROM WF_DOC_GW_FAWEN FW) D

WHERE A.NPROCID = B.NPROCID AND

A.NDOCID = D.NDOCID AND

A.NDOCSORTID = C.NDOCSORTID AND

C.NDOCSORTID IN (1, 2) AND

(A.NSTATE = 0 OR (A.NSTATE = 2 AND A.NDOCSORTID = 1)) AND

((((INSTR(‘,’ || A.CPROCUSERLIST || ‘,’,

‘,’ || 31601 || ‘,’) > 0 ) OR

(((27301 = A.RCV_ORGID OR

27301 = A.RCV_ENTITYID) OR

(27301 = A.TEMPORGID OR

27301 = A.TEMPORGID)) AND 20 = A.RCV_ROLEID))) OR

A.NPROCUID = 31601) AND

(A.NMSGID = 0 OR (A.NMSGID IS NOT NULL AND A.NFWQBOPT = 10)) AND

(A.CURTITLE IS NOT NULL) AND

((B.NPROCID = 20 AND A.NPROCSTATUS = 1) OR (B.NPROCID <> 20))

ORDER BY A.DMODIFYDATE DESC;

從業務上看，這條SQL最終的結果集只有幾條記錄，而WF_DOC_GW_SHOUWEN和WF_DOC_GW_FAWEN表的數據量都比較多，有上千萬條，而這兩張表只是為了取字段的內容，沒有過濾任何數據，于是想到，應該把謂詞推入到視圖中，這樣就能用到索引，避免了全表掃描

Sql代碼

SELECT /*+ push_pred(d)*/ ?DISTINCT A.CURTITLE AS CTITLE,

A.DMODIFYDATE,

A.NDOCID AS NDOCID,

A.NPROCID AS NPROCID,

B.CPROCNAME AS CPROCNAME,

B.NDAYS AS TRUE_DAYS,

(SYSDATE – A.DMODIFYDATE) AS DAYSLEFT,

A.NDOCSORTID AS NDOCSORTID,

A.NPROCSTATUS AS NPROCSTATUS,

C.CNAME AS DOCSORTNAME,

NVL(D.NJJCD, 0) NJJCD,

D.CDOCFROM AS CDOCFROM,

D.CDOCPRIORITY AS CDOCPRIORITY,

D.CWENHAO,

A.NFWQBOPT,

D.DW

FROM WF_DOC_GW A,

WF_PROCNAME B,

WF_DOCSORT C,

(SELECT ? NVL(CFWZH, ”) AS CWENHAO,

NVL(CFWDW, ‘ ‘) AS DW,

NDOCID,

NJJCD,

NVL(CDOCFROM, ‘ ‘) AS CDOCFROM,

NVL(CDOCPRIORITY, 0) AS CDOCPRIORITY

FROM WF_DOC_GW_SHOUWEN SW

UNION ALL

SELECT NVL(CWENHAO, ‘ ‘) AS CWENHAO,

NVL(CFWDW, ”) AS DW,

NDOCID,

NJJCD,

NVL(CDOCFROM, ‘本單位發文’) AS CDOCFROM,

NVL(CDOCPRIORITY, 0) AS CDOCPRIORITY

FROM WF_DOC_GW_FAWEN FW) D

WHERE A.NPROCID = B.NPROCID AND

A.NDOCID = D.NDOCID AND

A.NDOCSORTID = C.NDOCSORTID AND

C.NDOCSORTID IN (1, 2) AND

(A.NSTATE = 0 OR (A.NSTATE = 2 AND A.NDOCSORTID = 1)) AND

((((INSTR(‘,’ || A.CPROCUSERLIST || ‘,’,

‘,’ || 31601 || ‘,’) > 0 ) OR

(((27301 = A.RCV_ORGID OR

27301 = A.RCV_ENTITYID) OR

(27301 = A.TEMPORGID OR

27301 = A.TEMPORGID)) AND 20 = A.RCV_ROLEID))) OR

A.NPROCUID = 31601) AND

(A.NMSGID = 0 OR (A.NMSGID IS NOT NULL AND A.NFWQBOPT = 10)) AND

(A.CURTITLE IS NOT NULL) AND

((B.NPROCID = 20 AND A.NPROCSTATUS = 1) OR (B.NPROCID <> 20))

ORDER BY A.DMODIFYDATE DESC

只是加了一個hints /*+ push_pred(d)*/，時間從2秒降到了46毫秒，邏輯讀也降了一半，執行計劃太長，這里就不貼了，本著精益求精的態度，最后應該把中間過程的nvl函數也去掉

總結

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