1. Union
Syntax:
-- union 10 records select * from Table1 union select * from Table2 -- select EnglishProductName from Table1 union select EnglishProductName from Table2
Analysis:
You can union more than two tables --- simply add more Union operators and Select statements. A union is not the same as a join. A join puts the tables together horizontally, usually based on a primary-to-foreign-key relationship --- it’s for creating a single result from often dissimilar tables (denormalization). A union appends tables; is puts them together vertically --- it’s for creating a single result from similar tables.
2. Union All
Syntax:
-- union all 11 records select * from Table1 union all select * from Table2
Analysis:
The record that is common to both tables. The union operator suppresses duplicates, while union all does not.
3. Intersect
Syntax:
-- intersect 1 record select * from Table1 intersect select * from Table2
Analysis:
Intersect returns the common record from the two tables. It shows just one copy of the record, not both of them. This is a simple, yet powerful, set operation to see if you have the same data in more than one table.
4. Except
Syntax:
-- except 8 records select * from Table1 except select * from Table2
Analysis:
Except is showing all of the records from Table1 that do not also appear in Table2. Please not that Table1 is the first table in the query.