合并SQL中相同表的列

Question

I'm having difficulty finding a solution to this problem, as searching for merging SQL columns or adding columns from table gives a wide variety of results I don't want. It's much easier for me to illustrate with an example.

I have two tables:

Table 1

ColA  ColB  ColC
0     A     AL
1     B     DZ

Table 2

ColA  ColB  ColC
2     C     IS
3     D     KA

I want to merge these tables so the similar columns are basically combined, so I've got a new table with the same structure, and all of the values. So the output would be:

Output

ColA  ColB  ColC
0     A     AL
1     B     DZ
2     C     IS
3     D     KA

The issue is I want to find the distinct values across these columns from two similarly structured tables, so I cannot see how I can use a join for this, as if I join on any one value the other values will be lost, and a multiple-field join doesn't seem to work.

Answer 1

If you want to keep duplicate rows you could use UNION ALL and if you want to remove duplicate rows from result set you could use UNION in following:

SELECT ColA, ColB, ColC
FROM Table1

UNION ALL

SELECT ColA, ColB, ColC
FROM Table2 

Note that UNION ALL working faster than UNION

Answer 2

select ColA, ColB, ColC from table1
union 
select ColA, ColB, ColC from table2 

Answer 3

The union operator allows you to place the result of one query after the other, and eliminates duplicates:

SELECT cola, colb, colc
FROM   table1
UNION
SELECT cola, colb, colc
FROM   table2

Answer 4

select ColA, ColB, ColC from table1
union 
select ColA, ColB, ColC from table2 

You can also use UNION ALL