SQL UNION ALL

The SQL UNION ALL query is similar to SQL UNION query, it’s also used to merge two or more SQL SELECT query results. The difference is that SQL UNION returns distinct values, while SQL UNION ALL returns ALL the values.

SQL UNION ALL Query Syntax

SELECT Column(s) FROM Table1
UNION ALL
SELECT Column(s) FROM Table2

SQL UNION ALL Query Example

Table: FinanceEmployees

Table: DevelopmentEmployees

Select all the employees in FinanceEmployees and DevelopmentEmployees:

SELECT EmployeeId, FirstName, LastName FROM FinanceEmployees 
UNION ALL
SELECT EmployeeId, FirstName, LastName FROM DevelopmentEmployees

The result will look like:

We can see that the result-set has duplicated rows.