Question

所以我做了一个简单的查询，给出了一些案例的总和，其中提到了PassportNumber ='C_AA8'。但是如果我设置了在RegistrationCase中不存在的PassportNumber的查询，它将返回0（据我所知它不能JOIN）。我该如何解决？还有一种方法可以重新编译此查询以使用GROUP BY吗？感谢您的任何进一步帮助。我正在使用PHP与PHPmyadmin和AMPPS。固定寄存器。

SELECT COUNT( unRegisterCase.PassportNumber ) + COUNT( RegistrationCase.PassportNumber ) + COUNT( RecoveringCase.NewPassportNumber ) AS result
FROM RegistrationCase
LEFT JOIN unRegisterCase ON unRegisterCase.PassportNumber = RegistrationCase.Passportnumber
LEFT JOIN RecoveringCase ON RecoveringCase.NewPassportNumber = RegistrationCase.Passportnumber
WHERE RegistrationCase.PassportNumber =  'C_AA8'

Answer 1

不是吗？

SELECT COUNT(PassportNumber ) as PassportCount FROM
(
SELECT PassportNumber FROM RegistrationCase UNION ALL
SELECT NewPassportNumber FROM RecoveringCase UNION ALL
SELECT PassportNumber FROM unRegisterCaseber
) A
WHERE PassportNumber =  'C_AA8'

Answer 2

与SQl底部的where子句一起取消左连接，

试试这个

 SELECT COUNT( UnregisterCase.PassportNumber ) + 
        COUNT( RegistrationCase.PassportNumber ) + 
        COUNT( RecoveringCase.NewPassportNumber ) AS result
 FROM RegistrationCase, unRegisterCase, RecoveringCase
 WHERE UnregisterCase.PassportNumber = RegistrationCase.Passportnumber
 AND RecoveringCase.NewPassportNumber = RegistrationCase.Passportnumber
 AND RegistrationCase.PassportNumber =  'C_AA8'

同时检查区分大小写，因为您有不同的unRegister和Unregister

拼写

计数，加入或可能是GROUP By

2 个答案: