就“技能名称”的子查询选择而言，以下查询相当慢。当我运行一个针对 SQL 执行的配置文件时，我从 ACDCallinformation 表的每行中获得了太多针对技能名称子查询的查询。

优化此 SQL 查询的最佳方法是什么？是否有 MySQL 工具可帮助检查 SQL 查询的成本并优化脚本？

SELECT 
CASE 
    WHEN(
            SELECT 
                COUNT(ag.`PKEY`) - COUNT(ag.`ANSWERTIME`)
            FROM acdcallinformation ag
            WHERE (ag.`COMPLETED`) = 1 AND answertime IS NULL AND DATEofcall = DATE(NOW()) AND ag.skillid = acdcallinformation.skillid
        ) IS NULL 
    THEN 
            0 
    ELSE
        (
            SELECT COUNT(ag.`PKEY`) - COUNT(ag.`ANSWERTIME`)
                FROM acdcallinformation ag
            WHERE (ag.`COMPLETED`) = 1 AND answertime IS NULL AND DATEofcall= DATE(NOW()) AND ag.skillid = acdcallinformation.skillid) 
        END AS 'Lost Calls', 
        CASE WHEN COUNT(acdcallinformation.idleonqueue) IS NULL THEN 0 ELSE COUNT(acdcallinformation.idleonqueue) END AS 'Total Calls', 
        CASE WHEN COUNT(acdcallinformation.`ANSWERTIME`) IS NULL THEN 0 ELSE COUNT(acdcallinformation.`ANSWERTIME`) END AS 'Answered',
    (
        SELECT 
            skillinfo.skillname
        FROM skillinfo
        WHERE skillinfo.pkey = acdcallinformation.skillid
    ) AS Skill, 
    SEC_TO_TIME(AVG(TIME_TO_SEC(answertime)- TIME_TO_SEC(firstringonqueue))) AS 'Average Answer Time', 
    SEC_TO_TIME(AVG(TIME_TO_SEC(IDLEONQUEUE) - TIME_TO_SEC(answertime))) AS 'Average Talk Time'
FROM `acdcallinformation` acdcallinformation
WHERE DATEOFCALL = DATE(NOW())
GROUP BY skill;    

不确定显示数据的最佳方式:

ACDCALLINFORMATION - 当前行数 3028

INSTIME              PKEY   DATEOFCALL  CONNECTTIME FIRSTRING SKILLID
2012-07-19 14:50:16  19985  2012-07-19  14:50:16    14:50:16  5

SKILLINFO - 平均行数为 5-10

INSTIME              PKEY   SKILLNAME
2012-07-01 13:12:01  1      Calls Outgoing
2012-07-01 13:12:01  2      Call Centre
2012-07-01 13:12:01  3      Accounts
2012-07-01 13:12:01  4      Reception

这是预期的输出:

"Lost Calls"    "Total Calls"   "Answered"  "Skill"         "Average Answer Time" "Average Talk Time"

"1"         "2"          "1"            "Accounts"  "00:00:04"  "00:00:01"
"0"         "5"          "5"            "Service"   "00:00:07"  "00:01:20"

最佳答案

试试这个，使用内部连接来提高性能并避免不必要的子查询

SELECT 
    COALESCE(ag.skillcount, 0) AS 'Lost Calls', 
    CASE WHEN COUNT(acdcallinformation.idleonqueue) IS NULL THEN 0 ELSE COUNT(acdcallinformation.idleonqueue) END AS 'Total Calls', 
    CASE WHEN COUNT(acdcallinformation.`ANSWERTIME`) IS NULL THEN 0 ELSE COUNT(acdcallinformation.`ANSWERTIME`) END AS 'Answered',
    si.skillname AS Skill, 
    SEC_TO_TIME(AVG(TIME_TO_SEC(answertime)- TIME_TO_SEC(firstringonqueue))) AS 'Average Answer Time', 
    SEC_TO_TIME(AVG(TIME_TO_SEC(IDLEONQUEUE) - TIME_TO_SEC(answertime))) AS 'Average Talk Time'
FROM `acdcallinformation` acdcallinformation
LEFT JOIN (
    SELECT skillid,  COUNT(`PKEY`) - COUNT(`ANSWERTIME`) skillcount
    FROM acdcallinformation 
    WHERE (`COMPLETED`) = 1 AND answertime IS NULL AND DATEofcall = DATE(NOW())
) ag ON  AND ag.skillid = acdcallinformation.skillid
LEFT JOIN skillinfo si ON si.pkey = acdcallinformation.skillid
WHERE DATEOFCALL = DATE(NOW())
GROUP BY si.skillname;   

关于mysql - SQL - 对子查询的调用太多，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14755666/