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| 연산자 | 설명 |
|---|---|
| UNION | 중복을 제거한 집합 |
| UNION ALL | 중복을 제거하지 않은 집합 |
SELECT CustomerName AS Name, City, Country, 'CUSTOMER'
FROM Customers
UNION
SELECT SupplierName AS Name, City, Country, 'SUPPLIER'
FROM Suppliers
ORDER BY Name;
합집합
SELECT CategoryID AS ID FROM Categories
WHERE CategoryID > 4
UNION
SELECT EmployeeID AS ID FROM Employees
WHERE EmployeeID % 2 = 0;
-- UNION ALL로 바꿔볼 것
교집합
SELECT CategoryID AS ID
FROM Categories C, Employees E
WHERE
C.CategoryID > 4
AND E.EmployeeID % 2 = 0
AND C.CategoryID = E.EmployeeID;
차집합
SELECT CategoryID AS ID
FROM Categories
WHERE
CategoryID > 4
AND CategoryID NOT IN (
SELECT EmployeeID
FROM Employees
WHERE EmployeeID % 2 = 0
);
대칭차집합
SELECT ID FROM (
SELECT CategoryID AS ID FROM Categories
WHERE CategoryID > 4
UNION ALL
SELECT EmployeeID AS ID FROM Employees
WHERE EmployeeID % 2 = 0
) AS Temp
GROUP BY ID HAVING COUNT(*) = 1;