Question

我想看看对公交车的ETA做出的预测是否有实际消息。我写了这个查询，它超时了。难道我做错了什么？有什么优化可以帮到这里吗？

SELECT
P.ROUTE,
P.CODE,
(
    SELECT  COUNT(*)
    FROM    MESSAGE M
    WHERE   M.SENTDATE BETWEEN P.ARRIVAL-(20/60/24) AND P.ARRIVAL+(2/60/24)
    AND TRIM(SUBSTR(M.LOCATIONINFO, 3, 10))  = P.ROUTE
    AND TRIM(SUBSTR(M.LOCATIONINFO, 25, 10)) = P.CODE
)
CNT
FROM
(
    SELECT  *
    FROM    PREDICTION P
    WHERE   P.ARRIVAL BETWEEN TO_DATE('2012/07/04 04:30:00', 'YYYY/MM/DD HH24:MI:SS')   
    AND TO_DATE('2012/07/04 04:30:10', 'YYYY/MM/DD HH24:MI:SS')
    AND P.ROUTE ='7'
    AND P.CODE  ='2179'
)
P

Answer 1

要真正知道发生了什么，我们需要查看查询计划。在此期间，尝试重写您的查询以获得显式连接：

SELECT COUNT(*) as cnt
FROM (SELECT  *
      FROM PREDICTION P
      WHERE P.ARRIVAL BETWEEN TO_DATE('2012/07/04 04:30:00', 'YYYY/MM/DD HH24:MI:SS') AND TO_DATE('2012/07/04 04:30:10', 'YYYY/MM/DD HH24:MI:SS')AND
            P.ROUTE ='7' AND
            P.CODE  ='2179'
     ) P join
     MESSAGE M
     on M.SENTDATE BETWEEN P.ARRIVAL-(20/60/24) AND P.ARRIVAL+(2/60/24) AND
        TRIM(SUBSTR(M.LOCATIONINFO, 3, 10)) = P.ROUTE AND
        TRIM(SUBSTR(M.LOCATIONINFO, 25, 10)) = P.CODE

您正在进行相当复杂的加入。这两张桌有多大？他们有任何索引吗？

我建议尝试：

SELECT COUNT(*) as cnt
FROM (SELECT  *
      FROM PREDICTION P
      WHERE P.ARRIVAL BETWEEN TO_DATE('2012/07/04 04:30:00', 'YYYY/MM/DD HH24:MI:SS') AND TO_DATE('2012/07/04 04:30:10', 'YYYY/MM/DD HH24:MI:SS')AND
            P.ROUTE ='7' AND
            P.CODE  ='2179'
     ) P join
     MESSAGE M
     on M.SENTDATE BETWEEN P.ARRIVAL-(20/60/24) AND P.ARRIVAL+(2/60/24) AND
        TRIM(SUBSTR(M.LOCATIONINFO, 3, 10)) = '7' AND
        TRIM(SUBSTR(M.LOCATIONINFO, 25, 10)) = '2179'

这些是等效的。但是，在最初的情况下，Oracle可能会看到一个复杂的三部分连接，而不是使用正确的索引。在第二种情况下，它应该使用SENTDATE索引，这应该加速查询。

Answer 2

试试这个，看看它是否解决了问题（并且结果是正确的！）：

SELECT COUNT(M.*) CNT
FROM
    PREDICTION P
INNER JOIN
    MESSAGE M
ON  M.SENTDATE BETWEEN P.ARRIVAL-(20/60/24) AND P.ARRIVAL+(2/60/24)
AND TRIM(SUBSTR(M.LOCATIONINFO, 3, 10))  = P.ROUTE                         
AND TRIM(SUBSTR(M.LOCATIONINFO, 25, 10)) = P.CODE  
WHERE P.ARRIVAL BETWEEN TO_DATE('2012/07/04 04:30:00', 'YYYY/MM/DD HH24:MI:SS') AND TO_DATE('2012/07/04 04:30:10', 'YYYY/MM/DD HH24:MI:SS')                         
AND P.ROUTE ='7'                         
AND P.CODE  ='2179'

Answer 3

除了将查询更改为使用连接而不是子查询（如已建议的那样）之外，您还可以尝试

在路由和代码的比较中摆脱trim（substr（...）），因为这会使locationinfo上的任何索引无用
摆脱7和2179左右的引号（假设路线和代码是数字字段）

Oracle中的查询超时

3 个答案: