Question

对于像这样的查询

$query = "
SELECT t1.title, t1.content, t2.image, t2.tags
FROM blog1posts t1, blog1imagestags t2 
WHERE id = :id

UNION ALL

SELECT t1.title, t1.content, t2.image, t2.tags
FROM blog2posts t1, blog2imagestags t2 
WHERE id = :id

UNION ALL //THE PROBLEM

SELECT t1.title, t1.content, t2.tags
FROM blog2posts t1, blog3imagestags t2
WHERE id = :id
";

我如何使用查询联合或加入最后一部分？

Answer 1

你可以尝试这个（在第三个UNION中添加一个虚拟字段）：

SELECT t1.title, t1.content, t2.image, t2.tags
FROM blog1posts t1, blog1imagestags t2 
WHERE id = :id

UNION ALL

SELECT t1.title, t1.content, t2.image, t2.tags
FROM blog2posts t1, blog2imagestags t2 
WHERE id = :id

UNION ALL 

SELECT t1.title, t1.content, '' AS image, t2.tags
FROM blog2posts t1, blog3imagestags t2
WHERE id = :id

UNION和JOIN 3表，其中一个表没有相同的行号

1 个答案: