Question

这是我的UNION ALL查询，但它不起作用，我不知道为什么，这似乎是正确的

        SELECT 
                ID AS IDzivotinja, zivotinja 
                FROM zivotinje WHERE IDveterinar=$ID
        UNION ALL
        SELECT 
                ID AS IDsimptom, simptom 
                FROM simptomi WHERE IDveterinar=$ID
        UNION ALL
        SELECT
                ID AS IDterminza, terminza
                FROM termniniza WHERE IDveterinar=$ID

Answer 1

请注意，UNION中的每个SELECT语句必须具有相同的列数。列还必须具有类似的数据类型。此外，每个SELECT语句中的列必须具有相同的顺序。以下SQL查询应该起作用。请试一试。

编辑：如果相应的列没有相同的数据类型，您可以将它们转换为相同的数据类型，如下所示：

 SELECT 
        ID AS IDzivotinja, CAST(zivotinja AS CHAR) AS Col2
        FROM zivotinje WHERE IDveterinar=$ID
UNION ALL
SELECT 
        ID AS IDzivotinja, CAST(simptom  AS CHAR) AS Col2
        FROM simptomi WHERE IDveterinar=$ID
UNION ALL
SELECT
        ID AS IDzivotinja, CAST(terminza AS CHAR) AS Col2
        FROM termniniza WHERE IDveterinar=$ID

Answer 2

列必须相互匹配。

SELECT  ID, zivotinja as ColName, 'zivotinje' tableName
FROM    zivotinje 
WHERE   IDveterinar=$ID
UNION ALL
SELECT  ID, simptom as ColName, 'simptomi' tableName
FROM    simptomi 
WHERE   IDveterinar=$ID
UNION ALL
SELECT  ID, terminza as ColName, 'termniniza' tableName
FROM    termniniza 
WHERE   IDveterinar=$ID

还有一件事，这只是猜测。

如果列zivotinja，simptom，terminza只是用户定义值（，其目的是用于定义值来自哪个表的位置< / em>）然后你需要用单引号包装它。

SELECT ID, 'zivotinja' as ColName FROM zivotinje WHERE IDveterinar=$ID UNION ALL SELECT ID, 'simptom' as ColName FROM simptomi WHERE IDveterinar=$ID UNION ALL SELECT ID, 'terminza' as ColName FROM termniniza WHERE IDveterinar=$ID

UNION查询不起作用

2 个答案: