Drill down to SQL Server merge related operations Union,except,intersect detailed _mssql

There are several treatments for the result set that are worth explaining
1. and set (Union,union all)
This is very simple, is to combine two result set level. For example
SELECT * from A
UNION
SELECT * from B
Note Union deletes duplicate values, that is, duplicate rows in a and B end up only once, while union all retains duplicate rows.

2. Variance (Except)
is a two-part set that does not repeat. For example
SELECT * from A
EXCEPT
SELECT * from B
This means that the rows of a table that do not appear in table B.


3. Intersection (INTERSECT)
is a common part of two. For example
SELECT * from A
INTERSECT
SELECT * from B
This means that the records that appear in both A and B