MResult Services IT Analyst Interview Questions and Answers

Union combines and removes duplicates, Union All combines all rows including duplicates.

• Union removes duplicate rows, Union All does not

• Union is slower as it has to remove duplicates, Union All is faster

• Union requires the same number of columns in both queries, Union All does not

• Example: SELECT column1 FROM table1 UNION SELECT column1 FROM table2;

• Example: SELECT column1 FROM table1 UNION ALL SELECT column1 FROM table2;