JOINS and UNION Examples - SQL Query

What is the difference between JOINS and UNION.

Joins: A join is used to display columns with the same or different names from different tables. All columns are shown individually in the output.

Union: The UNION operator is used to combine data from two tables with same data type. When UNION is performed, the data from both tables will be collected in a single column which has a same data type.

Example: UNION Operator.

Consider the following tables.

Table1: Supplier

Supplier_IDSupplier_Name
100Samsung
200Sony
300Micromax

Table2: Orders

Order_IDSupplier_ID
1200
2400
3500
4600

Q. Write a query to perform UINON on column 'Customer_ID' from Table1 and Table2.

Answer:

SELECT Supplier_ID FROM Supplier
UNION
SELECT Supplier_ID FROM Orders
ORDER BY Supplier_ID


This query will show the union of Supplier_ID column.

Output:

Supplier_ID
100
200
300
400
500
600

Note: The union operator is used to avoid duplication of records. So the value 200 which is appear in the column Supplier_ID which is present in the both tables is displayed only once to avoid duplication.