--先申明個變量 。
DECLARE @Num INT;
SET @Num=0;

1. IF 語句

IF(@Num=0)
BEGIN
            PRINT('Num value is '+CAST(@Num AS VARCHAR(4)));
END

2. WHILE 語句（當......的時候，執行循環體）

WHILE(@Num<>0)
BEGIN
            PRINT('Num value is '+CAST(@Num AS VARCHAR(4)));
END

3. CASE 語句（特殊）

--創建測試臨時表
IF(OBJECT_ID('tempdb..#Books') IS NOT NULL)
BEGIN
            DROP TABLE #Books;
END

CREATE TABLE #Books
(
            BookName NVARCHAR(20),
            BookCode NVARCHAR(20)
)

INSERT INTO #Books( BookName, BookCode ) VALUES(N'C# 本質論','JC556874');
INSERT INTO #Books( BookName, BookCode ) VALUES(N'JS 本質論','JS556874');

--簡單 Case 函數
SELECT
(
 CASE BookCode
             WHEN 'JC556874' THEN 'C#' 
             WHEN 'JS556874' THEN 'JS'
 END
) CustFiled
FROM #Books

--搜索 Case 函數
SELECT
(
 CASE 
           WHEN BookCode LIKE '%C%' THEN 'C#'
           WHEN BookCode LIKE '%S%' THEN 'JS'
 END
) CustFiled
FROM #Books

CASE 語句還可以放在 WHERE,GROUP 等中