Basic Difference Between Union vs Union All Operator

Union: It is an Operator which is used to combine two or more tables.
It gives a unique result set and it will not allow duplicates.

Basic Conditions which need to be fulfilled by tables.

1. Both tables should have the same number of columns.
2. Both table columns should have the same data types.
3. Columns should be in the same order in each table.

Let's take an Example: 

We have 2 tables containing employee id and employee name and it has some duplicate values as well.

Table: Employee1

Table: Employee2

Query:     Select  from Employee1 Union Select  from Employee2;

After Using Union Operator We will get only 8 records instead of 10 because we have 2 duplicates in Table 2.

Union All: It is an operator which works the same as the Union operator and it also allows duplicate values.

Query:     Select  from Employee1 Union All Select  from Employee2;

After Using Union All Operator We will get 10 records which include 2 duplicate values.

Thanks for reading this and I hope you like it.

Mayank Agrawal