我有一个 mysql 查询,当我使用 where 子句时它工作正常,但当我不使用时 where 子句消失了,从不给出输出,最后超时。 实际上,我使用了 Explain 命令来检查查询的性能,在这两种情况下,Explain 给出了用于连接的相同行数。 我附上了使用 Explain 命令获得的输出图像。 下面是查询。 我不知道这里有什么问题。 非常感谢任何帮助。 谢谢。
SELECT
MCI.CLIENT_ID AS CLIENT_ID, MCI.NAME AS CLIENT_NAME, MCI.PRIMARY_CONTACT AS CLIENT_PRIMARY_CONTACT,
MCI.ADDED_BY AS SP_ID, CONCAT(MUD_SP.FIRST_NAME, ' ', MUD_SP.LAST_NAME) AS SP_NAME,
MCI.FK_PROSPECT_ID AS PROSPECT_ID, MCI.DATE_ADDED AS ADDED_ON,
(SELECT GROUP_CONCAT(LT.TAG_TEXT SEPARATOR ', ')
FROM LK_TAG LT
INNER JOIN M_OBJECT_TAG_MAPPING MOTM
ON LT.PK_ID = MOTM.FK_TAG_ID
WHERE MOTM.FK_OBJECT_ID = MCI.FK_PROSPECT_ID
AND MOTM.OBJECT_TYPE = 1
AND MOTM.IS_ACTIVE = 1
) AS TAGS,
IFNULL(SUM(GET_DIGITS(MMR.RCP_AMOUNT)), 0) AS REVENUE_SO_FAR,
IFNULL(SUM(GET_DIGITS(MMR.RCP_RUPEES)), 0) AS REVENUE_INR,
COUNT(DISTINCT PMI_MONTHLY.PROJECT_ID) AS MONTHLY,
COUNT(DISTINCT PMI_FIXED.PROJECT_ID) AS FIXED,
COUNT(DISTINCT PMI_HOURLY.PROJECT_ID) AS HOURLY,
COUNT(DISTINCT PMI_ANNUAL.PROJECT_ID) AS ANNUAL,
COUNT(DISTINCT PMI_CURRENTLY_RUNNING.PROJECT_ID) AS CURRENTLY_RUNNING_PROJECTS,
COUNT(DISTINCT PMI_YET_TO_START.PROJECT_ID) AS YET_TO_START_PROJECTS,
COUNT(DISTINCT PMI_TECH_SALES_CLOSED.PROJECT_ID) AS TECH_SALES_CLOSED_PROJECTS
FROM
M_CLIENT_INFO MCI
INNER JOIN M_USER_DETAILS MUD_SP
ON MCI.ADDED_BY = MUD_SP.PK_ID
LEFT OUTER JOIN M_MONTH_RECEIPT MMR
ON MMR.CLIENT_ID = MCI.CLIENT_ID
LEFT OUTER JOIN M_PROJECT_INFO PMI_FIXED
ON PMI_FIXED.CLIENT_ID = MCI.CLIENT_ID AND PMI_FIXED.PROJECT_TYPE = 1
LEFT OUTER JOIN M_PROJECT_INFO PMI_MONTHLY
ON PMI_MONTHLY.CLIENT_ID = MCI.CLIENT_ID AND PMI_MONTHLY.PROJECT_TYPE = 2
LEFT OUTER JOIN M_PROJECT_INFO PMI_HOURLY
ON PMI_HOURLY.CLIENT_ID = MCI.CLIENT_ID AND PMI_HOURLY.PROJECT_TYPE = 3
LEFT OUTER JOIN M_PROJECT_INFO PMI_ANNUAL
ON PMI_ANNUAL.CLIENT_ID = MCI.CLIENT_ID AND PMI_ANNUAL.PROJECT_TYPE = 4
LEFT OUTER JOIN M_PROJECT_INFO PMI_CURRENTLY_RUNNING
ON PMI_CURRENTLY_RUNNING.CLIENT_ID = MCI.CLIENT_ID AND PMI_CURRENTLY_RUNNING.STATUS = 4
LEFT OUTER JOIN M_PROJECT_INFO PMI_YET_TO_START
ON PMI_YET_TO_START.CLIENT_ID = MCI.CLIENT_ID AND PMI_YET_TO_START.STATUS < 4
LEFT OUTER JOIN M_PROJECT_INFO PMI_TECH_SALES_CLOSED
ON PMI_TECH_SALES_CLOSED.CLIENT_ID = MCI.CLIENT_ID AND PMI_TECH_SALES_CLOSED.STATUS > 4
WHERE YEAR(MCI.DATE_ADDED) = '2012'
GROUP BY MCI.CLIENT_ID ORDER BY CLIENT_NAME ASC
最佳答案
是的,正如许多人所说,关键是当您有 where 子句时,mysql 引擎会过滤表 M_CLIENT_INFO -- 可能是戏剧性的 --。
与删除 where 子句类似的结果是添加此 where 子句:
where 1 = 1
您会看到性能下降也是因为 mysql 将尝试获取所有数据。
关于没有 where 子句的 MySql 查询运行非常慢(实际上从不给出输出),我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/18996354/