Union
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- The union operator combines the results of two or more queries into a single result set. But no.of columns must match in both/all the queries (and also the order) which are used for union.
- We can union two tables irrespective of common field.
- The UNION set operator is used for combining data from two tables which have columns with the same datatype.
- Union – Returns with no duplicate rows.
- Union all – Retruns with duplicate rows (No. of rows returned = No. of rows in Query1 + No. of rows in Query 2).
- We cannot use the union operator within a create view statement.
- We cannot use the union operator on text and image columns.
Syntax
[pastacode lang=”sql” manual=”SELECT%20expression1%2C%20expression2%2C%20…%20expression_n%0AFROM%20tables%0A%5BWHERE%20conditions%5D%0AUNION%0ASELECT%20expression1%2C%20expression2%2C%20…%20expression_n%0AFROM%20tables%0A%5BWHERE%20conditions%5D%3B” message=”” highlight=”” provider=”manual”/]Join
- Joins are used to extract information from more than one table based on the related column/coloums (PK and RFK) any no. of rows can be retrived based on matching colums.
- We can join two tables by ‘join’ if they have common field.
- A Join is used for displaying columns with the same or different names from different tables.
- Different types of joins are Inner join=equi join=join , outer join (Right outer join/right join, Left outer join / left join), Cross join , and full outer join/outer join.
- We can use join operator within a create view statement.
- We can use the join operator on text and image columns.
