SQL Server常用关键字与功能详解

IF EXISTS (SELECT 1 FROM Users WHERE UserID = 1)
    PRINT 'User exists'
ELSE
    PRINT 'User does not exist'

SELECT IIF(Age >= 18, 'Adult', 'Minor') AS AgeGroup
FROM Users

SELECT 
    CASE 
        WHEN Age >= 18 THEN 'Adult'
        ELSE 'Minor'
    END AS AgeGroup
FROM Users

BEGIN
    PRINT 'Start of block'
    SELECT * FROM Users
END

DECLARE @Counter INT = 0
WHILE @Counter < 5
BEGIN
    PRINT @Counter
    SET @Counter = @Counter + 1
END

SELECT * FROM Users

INSERT INTO Users (UserID, UserName)
VALUES (1, 'John')

UPDATE Users SET UserName = 'Jane' WHERE UserID = 1

DELETE FROM Users WHERE UserID = 1

MERGE INTO TargetTable AS Target
USING SourceTable AS Source
ON Target.ID = Source.ID
WHEN MATCHED THEN
    UPDATE SET Target.Name = Source.Name
WHEN NOT MATCHED BY TARGET THEN
    INSERT (ID, Name) VALUES (Source.ID, Source.Name)
WHEN NOT MATCHED BY SOURCE THEN
    DELETE;

SELECT RTRIM('Hello   ') AS Trimmed

SELECT STUFF('abcdef', 2, 3, '123') AS Result -- 输出: a123ef

SELECT LEN('Hello') AS StringLength

SELECT POWER(2, 3) AS Result -- 输出: 8

SELECT DATEADD(DAY, 1, '2024-01-01') AS NextDay

SELECT DATEDIFF(DAY, '2024-01-01', '2024-01-10') AS DaysDifference

SELECT Name, Salary, RANK() OVER (ORDER BY Salary DESC) AS Rank
FROM Employees

SELECT Name, Department, RANK() OVER (PARTITION BY Department ORDER BY Salary DESC) AS Rank
FROM Employees

CREATE TABLE #TempTable (ID INT, Name NVARCHAR(50))
INSERT INTO #TempTable VALUES (1, 'John')
SELECT * FROM #TempTable

BEGIN TRAN
UPDATE Users SET Name = 'NewName' WHERE ID = 1
COMMIT

BEGIN TRAN
UPDATE Users SET Name = 'NewName' WHERE ID = 1
ROLLBACK

GRANT SELECT ON Users TO UserRole
REVOKE SELECT ON Users FROM UserRole

DENY SELECT ON Users TO UserRole

SELECT * FROM Users WITH (NOLOCK)

SELECT Name FROM Users FOR XML PATH('User')

SELECT * FROM Users u CROSS APPLY dbo.GetDetails(u.ID)