关于合并语法的MySQL条件

我有一个由合并语法组成的查询。COALESCE语法只是查找文件的审核日期。在WHERE语句中，我只想从

AuditDate

别名字段输出已审核的文件库，但我不工作。这是我的问题

SELECT COALESCE(qua.starttime, prd.starttime) AS `AuditDate`,
       prd.employeeno AS `EmployeeNo`,
       prd.starttime AS `StartTime`,
       prd.endtime AS `EndTime`
  FROM production prd
  LEFT JOIN qualityaudit qua
    ON prd.id=qua.id
 WHERE `AuditDate` BETWEEN '2011-10-01 00:00:00' AND '2011-10-01 23:59:59';

有人能帮助我如何正确处理此查询吗？

使用

SELECT COALESCE(qua.starttime, prd.starttime) AS `AuditDate`,
       prd.employeeno AS `EmployeeNo`,
       prd.starttime AS `StartTime`,
       prd.endtime AS `EndTime`
  FROM production prd
  LEFT JOIN qualityaudit qua
    ON prd.id=qua.id
 WHERE COALESCE(qua.starttime, prd.starttime) BETWEEN '2011-10-01 00:00:00' AND '2011-10-01 23:59:59';

---

以上假设您的日期格式/列类型确实匹配…

您的查询需要如下所示

SELECT COALESCE(qua.starttime, prd.starttime) AS `AuditDate`,
       prd.employeeno AS `EmployeeNo`,
       prd.starttime AS `StartTime`,
       prd.endtime AS `EndTime`
  FROM production prd
  LEFT JOIN qualityaudit qua
    ON prd.id=qua.id
 WHERE COALESCE(qua.starttime, prd.starttime) BETWEEN '2011-10-01 00:00:00' AND '2011-10-01 23:59:59';

对于您的情况，您不能在

WHERE

子句中将来自函数结果的别名用作查询条件（请参阅）。但是您可以使用别名在

HAVING

子句中搜索，因为MySQL 5.0.2和更高版本允许

HAVING

子句引用select列表或外部子查询中select表达式中命名的任何列或别名，并聚合函数，如

SELECT COALESCE(qua.starttime, prd.starttime) AS `AuditDate`,
       prd.employeeno AS `EmployeeNo`,
       prd.starttime AS `StartTime`,
       prd.endtime AS `EndTime`
  FROM production prd
  LEFT JOIN qualityaudit qua
    ON prd.id=qua.id
 HAVING `AuditDate` BETWEEN '2011-10-01 00:00:00' AND '2011-10-01 23:59:59';

---

两者的结果相同

您不能使用

WHERE

子句中

SELECT

列表中的别名

使用以下命令：

SELECT *
FROM
  ( SELECT COALESCE(qua.starttime, prd.starttime) AS `AuditDate`,
           prd.employeeno AS `EmployeeNo`,
           prd.starttime AS `StartTime`,
           prd.endtime AS `EndTime`
      FROM production prd
      LEFT JOIN qualityaudit qua
        ON prd.id=qua.id
  ) AS tmp
WHERE `AuditDate` BETWEEN '2011-10-01 00:00:00' AND '2011-10-01 23:59:59';

或复制代码：

SELECT COALESCE(qua.starttime, prd.starttime) AS `AuditDate`,
       prd.employeeno AS `EmployeeNo`,
       prd.starttime AS `StartTime`,
       prd.endtime AS `EndTime`
  FROM production prd
  LEFT JOIN qualityaudit qua
    ON prd.id=qua.id
 WHERE COALESCE(qua.starttime, prd.starttime) 
         BETWEEN '2011-10-01 00:00:00' AND '2011-10-01 23:59:59';

---

您不能像其他人指出的那样使用别名。为了避免两次调用coalesce，可以使用HAVING语句

SELECT COALESCE(qua.starttime, prd.starttime) AS `AuditDate`,
       prd.employeeno AS `EmployeeNo`,
       prd.starttime AS `StartTime`,
       prd.endtime AS `EndTime`
  FROM production prd
  LEFT JOIN qualityaudit qua
    ON prd.id=qua.id
HAVING `AuditDate` BETWEEN '2011-10-01 00:00:00' AND '2011-10-01 23:59:59';

---

你能比“它不工作”更具体一些吗？谢谢你的帮助，这个查询很好，我不需要创建子查询。谢谢你的帮助，这个查询很好，我不需要创建子查询。谢谢你的帮助，这个查询很好，我不需要创建子查询。谢谢你的帮助，这个查询工作正常，我不需要创建子查询。