本文介绍了添加列以说明联合结果来自哪个表的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
当我使用 UNION
命令搜索多个表时,如何选择每个结果来自哪个表?
How can I select which table each result is from, when I use a UNION
command to search multiple tables?
例如,如果两个表都有结果,我如何添加一列来说明(或区分)它是来自 tableA 还是 tableB.
For example, if there are results from both tables, how can I add a column that will say (or differentiate between) whether it is from tableA or tableB.
推荐答案
试试这个,只需添加一个虚拟列作为表名.
try this one, simply add a virtual column for the name of the table.
SELECT *
FROM
(
SELECT *, 'tableA' as tableName FROM tableA
UNION ALL
SELECT *, 'tableB' as tableName FROM tableB
UNION ALL
SELECT *, 'tableC' as tableName FROM tableC
) s
WHERE colName = 'hello'
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