数据库：如何分离来自两个表的sql查询？

I have an SQL query which uses UNION in order to obtain data from two tables. I need a way to find out which data is coming from which table in the UI. Is there a way to insert a flag which could say about the data coming from a particular table ? I know that firing two queries may be a solution but I want to try and keep it in one query. Is there a solution ?

我有一个SQL查询，它使用UNION来从两个表中获取数据。我需要一种方法来找出哪些数据来自UI中的哪个表。有没有办法插入一个标志，可以说明来自特定表的数据？我知道解雇两个查询可能是一个解决方案，但我想尝试将其保存在一个查询中。有解决方案吗？

3 个解决方案

#1

You can try:

你可以试试：

  SELECT 'T1' as tbl, Field1,Field2,Field3 From TABLE1 UNION 
  SELECT 'T2' as tbl, Field1,Field2,Field3 From TABLE2

#2

If you are combining data from two tables, then you should be using UNION ALL, not UNION. UNION incurs overhead for removing duplicates, even if none exist.

如果要合并来自两个表的数据，那么您应该使用UNION ALL，而不是UNION。即使不存在重复项，UNION也会产生开销。

So:

所以：

select t1.*, 'table1' as which
from table1 t1
union all
select t2.*, 'table2'
from table2 t2;

The use of * presumes that the columns and types are identical/compatible in the two tables.

使用*假定列和类型在两个表中是相同/兼容的。

#3

SELECT 'table1' AS 'table', * FROM table1
UNION
SELECT 'table2' AS 'table', * FROM table2

#1