Tutorial by Examples

CREATE TABLE HR_EMPLOYEES ( PersonID int, LastName VARCHAR(30), FirstName VARCHAR(30), Position VARCHAR(30) ); CREATE TABLE FINANCE_EMPLOYEES ( PersonID INT, LastName VARCHAR(30), FirstName VARCHAR(30), Position VARCHAR(30) ); Let's say we want to ...

In simple terms: UNION joins 2 result sets while removing duplicates from the result set UNION ALL joins 2 result sets without attempting to remove duplicates One mistake many people make is to use a UNION when they do not need to have the duplicates removed. The additional performance cost...