MySQL查询-如何在另一个表中合并表

Question

连接结果列中的表时遇到问题。 我有一个有效的查询，该查询使用UNION合并了不同的表，但是当我扩展另一个表时，出现错误消息：“所用的SELECT语句具有不同的列数”

这是我的查询：

(SELECT
    IDNumber,
    CONCAT(LastName, ', ', FirstName, ' ', Middle) as Name,
    CONCAT(EmDesignation, ', ', Department) as Information,
    Image,
    v.PlateNo as PlateNumber
FROM
    tblemployee as e, tblvehicle as v
WHERE 
    v.RFIDNo LIKE '6424823943'
AND
    e.RFIDNo LIKE '6424823943')
UNION
(SELECT 
    IDNumber,
    CONCAT(LastName, ', ', FirstName, ' ', Middle) as Name,
    CONCAT(Course, ', ', Year) as Information,
    Image,
    v.PlateNo as PlateNumber
FROM
    tblstudents as s, tblvehicle as v
WHERE
    v.RFIDNo LIKE '6424823943'
AND
    s.RFIDNo LIKE '6424823943')

我有这个问题。 上面的继续查询

UNION
(SELECT
    Barrier
FROM 
    tblinformation as inf
WHERE
    inf.RFIDNo IN (6424823943)
ORDER BY 
    AttendanceNo DESC LIMIT 1)

Answer 1

错误消息指出问题所在。 只需提高SELECT中的列数，它将可以正常工作。

Answer 2

错误消息是正确的。 将NULL添加到第二个查询以匹配列号，它将起作用。

例如：

SELECT
    Barrier,
    NULL,
    NULL,
    NULL,
    NULL
FROM 
    tblinformation as inf
...