SQL UNION ALL

UNION ALL combines the result sets of multiple SELECT statements and returns all rows including duplicates.

The UNION ALL operator is used to combine the results of two or more SELECT queries into a single result set without removing duplicate rows.

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

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

SELECT CustomerName
FROM CustomersIndia
UNION ALL
SELECT CustomerName
FROM CustomersUSA;

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

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

-- Shows all orders, even if some OrderIDs repeat.

Exam/Interview Definition:
UNION ALL in SQL Server is used to combine the results of multiple SELECT queries and returns all rows including duplicate records.