mysql - GROUP_CONCAT 不同查询和子查询的性能问题

Question

我正在尝试在 MYSQL DB 中执行此查询。

SELECT FirstName,LastName
    CONCAT(COALESCE(Address1, ''),
    COALESCE(Address2, '')) AS Address2,
    (SELECT GROUP_CONCAT(EmpDept ' ') FROM EMP_DEPT
     USE INDEX (EMP_DEPT_IDX)
     WHERE EMP_DEPT.EMP_ID = EMP.EMP_ID) AS DEPT,
    COUNT(PIN) AS PIN,
    MIN(SALARY) AS SALARY,
    GROUP_CONCAT(DISTINCT PAY_CODE SEPARATOR ' ') AS PAYROLL_CODE
FROM EMP WHERE HOUSE='YELLOW' AND HOUSE_AREA='220'
    AND (JOIN_YEAR = '2011' OR JOIN_YEAR = '2012')
    AND EMP_BAND='G'
    AND (FRESHER = 'N' OR FRESHER = 'FALSE')   
    AND PIN IS NOT NULL
    AND SALARY > 0
GROUP BY FirstName,LastName Address3, Address2, DEPT

查询工作正常，我得到了所需的结果集。

唯一的问题是，使用 GROUP_CONCAT 编写的这两行代码对性能造成了巨大的影响，

 (SELECT GROUP_CONCAT(EmpDept ' ') FROM EMP_DEPT
    USE INDEX (EMP_DEPT_IDX)
    WHERE EMP_DEPT.EMP_ID = EMP.EMP_ID) AS DEPT


 GROUP_CONCAT(DISTINCT PAY_CODE SEPARATOR ' ') AS PAYROLL_CODE

我尝试添加 INDEX，但仍然没有成功。(只有这些子查询大约需要 30-40 秒来执行)

我尝试实现联接，但由于我是 mysql 新手，所以没有运气..

任何人都可以帮助我加快查询执行速度吗？

Answer 1

尝试用子查询替换带有外连接的相关子查询:

SELECT FirstName,LastName
    CONCAT(COALESCE(Address1, ''),
    COALESCE(Address2, '')) AS Address2,
    COALESCE(DEPT, '') AS DEPT,
    COUNT(PIN) AS PIN,
    MIN(SALARY) AS SALARY,
    GROUP_CONCAT(DISTINCT PAY_CODE SEPARATOR ' ') AS PAYROLL_CODE
FROM EMP 
LEFT JOIN (SELECT EMP_ID, GROUP_CONCAT(EmpDept SEPARATOR ' ') AS DEPT
           FROM EMP_DEPT
           GROUP BY EMP_ID) AS EMP_DEPT ON EMP_DEPT.EMP_ID = EMP.EMP_ID
WHERE HOUSE='YELLOW' AND HOUSE_AREA='220'
    AND (JOIN_YEAR = '2011' OR JOIN_YEAR = '2012')
    AND EMP_BAND='G'
    AND (FRESHER = 'N' OR FRESHER = 'FALSE')   
    AND PIN IS NOT NULL
    AND SALARY > 0
GROUP BY EMP.EMP_ID

另外，我改变了最后的GROUP BY使用EMP_ID列，而不是返回的列值。

也有可能只改变最后的 GROUP BY会解决你的问题。按索引列分组应该更有效，因此请确保您在 EMP_ID 上有索引.