将两个不同表中的数据合并到一个表中？

Question

我有以下两个表:

uid   | ABC   | ... (bunch of other stuff) ...
1     | val 1 | ... (bunch of other stuff) ...
2     | val 2 | ... (bunch of other stuff) ...
3     | val 3 | ... (bunch of other stuff) ...

和...

uid   | DEF   | ... (bunch of other stuff) ...
4     | val 4 | ... (bunch of other stuff) ...
5     | val 5 | ... (bunch of other stuff) ...
6     | val 6 | ... (bunch of other stuff) ...

我想最终......

uid   | text  | ... (bunch of other stuff) ...
1     | val 1 | ... (bunch of other stuff) ...
2     | val 2 | ... (bunch of other stuff) ...
3     | val 3 | ... (bunch of other stuff) ...
4     | val 4 | ... (bunch of other stuff) ...
5     | val 5 | ... (bunch of other stuff) ...
6     | val 6 | ... (bunch of other stuff) ...

这看起来很简单,但我似乎无法弄清楚如何做到这一点.这不是一个加入？是吗？

Answer 1

该UNION条款将在这里帮助您.它将两个或多个结果集合并为一个.

尝试:

SELECT uid, ABC, OtherStuff
FROM Table1

UNION

SELECT uid, DEF, OtherStuff
FROM Table2

UNION

SELECT uid, GHI, OtherStuff
FROM Table3

ORDER BY uid

这个主题与UNION ALL运营商有所不同. UNION将UNION ALL保留重复的行,同时保留它们.

这除了行中的简单差异之外还有其他结果:删除重复项,UNION运算符需要对最终结果集进行排序.这是UNION ALL运营商没有遇到的开销.此外,显式排序操作可能导致收集的结果集UNION与排序顺序不同UNION ALL.我建议您ORDER BY在收集结果集后使用显式语句,以确保您的排序顺序符合您的意图.

另请注意,列数必须与UNION编辑的结果集匹配.从OP中不清楚这两个表在它们存储的列数方面有何不同,所以我对UNION两个SELECT *语句之间的做法犹豫不决.