Union Vs. Union all

[AyubHussain]

What is difference between Union and Union all Operators?

[dsusmitha]

Union :

1.Union Set operator is used to fetch the records from 2 different tables which eliminates the duplicate records
2.Syntax:Select col1,col2…from table1;
Union
Select col1,col2…from table2
3.For Performance tuning Union operator is not preferable as it takes time to eliminate duplicate records

Union ALL :

1.Union all Set operator is used to fetch the records from 2 different tables which does not eliminates the duplicate records
2.Syntax:Select col1,col2…from table1;
Union
Select col1,col2…from table2;
3.Union all is preferable operator in Performance tuning.