COALESCE语法上的MySQL条件

Question

我有一个查询组合COALESCE语法。 COALESCE语法只需找到文件的审核日期。在我的WHERE语句中，我只想从AuditDate别名字段输出Audited File base，但我不工作。这是我的查询。

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'; 

任何人都可以帮助我如何得到这个查询正确吗？

Answer 1

您的查询需要是这样

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'; 

您的具体情况，你可以在WHERE子句中使用函数结果的别名作为查询条件（请参阅http://dev.mysql.com/doc/refman/5.0/en/problems-with-alias.html）。但是您可以使用别名在HAVING子句中搜索，因为MySQL 5.0.2和最多允许HAVING子句引用在SELECT列表或外部子查询中的select_expr中指定的任何列或别名，并且聚合函数，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'; 

都具有相同的结果

Answer 2

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'; 

以上假设你的日期格式/列类型匹配真的...

Answer 3

不能在WHERE子句中使用别名从SELECT列表。

使用此：

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'; 

或重复的代码：

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'; 

Answer 4

正如其他人指出，你不能使用别名。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';