SQL UNION

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UNION is used to combine the results of multiple SELECT statements into one result set while removing duplicate records.

The UNION operator is used to combine the results of two or more SELECT queries into a single result set. It removes duplicate rows automatically.

Rules for Using UNION:
1️. The number of columns must be the same in all SELECT statements.
2️. The data types must be compatible.
3️. The column order must match.

Syntax 

SELECT column1, column2
FROM table1
UNION
SELECT column1, column2
FROM table2;

Example: 

SELECT CustomerID, CustomerName
FROM CustomersIndia
UNION
SELECT CustomerID, CustomerName
FROM CustomersUSA;

Example: UNION with ORDER BY

SELECT CustomerName
FROM CustomersIndia
UNION
SELECT CustomerName
FROM CustomersUSA
ORDER BY CustomerName;

Example: Combine online orders and store orders:

SELECT OrderID, ProductName
FROM OnlineOrders
UNION
SELECT OrderID, ProductName
FROM StoreOrders;


Interview Definition:
UNION in SQL Server combines the results of two or more SELECT queries into one result set and removes duplicate rows.

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