Sql 将左连接转换为简单连接
我的左联接子查询花费的时间更长。我如何隐藏它以加入Sql 将左连接转换为简单连接,sql,join,subquery,Sql,Join,Subquery,我的左联接子查询花费的时间更长。我如何隐藏它以加入 SELECT * FROM "TABLE_A" LEFT OUTER JOIN TABLE_B ON TABLE_A.mainid = TABLE_B.secondID LEFT JOIN (
SELECT * FROM "TABLE_A"
LEFT OUTER JOIN TABLE_B ON TABLE_A.mainid = TABLE_B.secondID
LEFT JOIN (
SELECT secondID
FROM TABLE_C
WHERE thirdID = 21
) Z ON TABLE_A.mainid = Z.secondID
WHERE "TABLE_A"."TRUEID" = 9
AND ((TABLE_A.USERNO IN (23))
首先,更简洁地编写查询:
SELECT *
FROM "TABLE_A" a LEFT JOIN
TABLE_B b
ON a.mainid = b.secondID LEFT JOIN
TABLE_C c
ON a.mainid = c.secondID AND c.thirdID = 21
WHERE a."TRUEID" = 9 AND a.USERNO IN (23);
然后考虑指标:
表A(TRUEID、USERNO、mainid)
Table_B(secondID)
Table_C(secondID,thirdID)