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SQL | UNION Operator

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  • Difficulty Level : Basic
  • Last Updated : 28 Aug, 2020
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The UNION operator could be used to find the result-set or combination of two or more tables.

Terms and Condition for using UNION :

  • Each table used within UNION must have the same number of columns.
  • The columns must have same data types.
  • The columns in each table must be in the same order.

1. UNION Syntax :

SELECT columnnames FROM table1
UNION
SELECT columnnames FROM table2;

UNION operator provides only unique values by default. To find duplicate values, use UNION ALL :

2. UNION ALL Syntax :

SELECT columnnames FROM table1
UNION ALL
SELECT columnnames FROM table2;

Let’s assume we have two tables “Geeks1” and “Geeks2”;

Select * 
from Geeks1; 

IDNameSalaryCity
1234Khushi23000Jaipur
2345Megha24000Delhi
3456Komal24500Noida

Select * 
from Geeks2; 

IDNameSalaryCity
5678Vikram26000Gurugram
6789Mahesh24500Noida
7890Ashish25600Delhi

SQL UNION Example –
The below SQL statement finds the cities (only unique values) from both the “Geeks1” and the “Geeks2” table :

Example –

SELECT City 
FROM Geeks1

UNION

SELECT City 
FROM Geeks2
ORDER BY City; 

Output –

City
Delhi
Gurugram
Jaipur
Noida

SQL UNION ALL Example –
The below SQL statement finds the cities (duplicate values also) from both the “Geeks1” and the “Geeks2” table :

Example –

SELECT City 
FROM Customers

UNION ALL

SELECT City 
FROM Suppliers
ORDER BY City; 

Output –

City
Delhi
Delhi
Gurugram
Jaipur
Noida
Noida

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