SQL Server2008數據庫導入導出兼容性處置計劃。本站提示廣大學習愛好者：（SQL Server2008數據庫導入導出兼容性處置計劃）文章只能為提供參考，不一定能成為您想要的結果。以下是SQL Server2008數據庫導入導出兼容性處置計劃正文
1. CASE WHEN 表達式有兩種情勢
--簡略Case函數
CASE sex
WHEN '1' THEN '男'
WHEN '2' THEN '女'
ELSE '其他' END
--Case搜刮函數
CASE
WHEN sex = '1' THEN '男'
WHEN sex = '2' THEN '女'
ELSE '其他' END
2. CASE WHEN 在語句中分歧地位的用法
2.1 SELECT CASE WHEN 用法
SELECT grade, COUNT (CASE WHEN sex = 1 THEN 1 /*sex 1為男生，2位女生*/
ELSE NULL
END) 男生數,
COUNT (CASE WHEN sex = 2 THEN 1
ELSE NULL
END) 女生數
FROM students GROUP BY grade;
2.2 WHERE CASE WHEN 用法
SELECT T2.*, T1.*
FROM T1, T2
WHERE (CASE WHEN T2.COMPARE_TYPE = 'A' AND
T1.SOME_TYPE LIKE 'NOTHING%'
THEN 1
WHEN T2.COMPARE_TYPE != 'A' AND
T1.SOME_TYPE NOT LIKE 'NOTHING%'
THEN 1
ELSE 0
END) = 1
2.3 GROUP BY CASE WHEN 用法
SELECT
CASE WHEN salary <= 500 THEN '1'
WHEN salary > 500 AND salary <= 600 THEN '2'
WHEN salary > 600 AND salary <= 800 THEN '3'
WHEN salary > 800 AND salary <= 1000 THEN '4'
ELSE NULL END salary_class, -- 別號定名
COUNT(*)
FROM Table_A
GROUP BY
CASE WHEN salary <= 500 THEN '1'
WHEN salary > 500 AND salary <= 600 THEN '2'
WHEN salary > 600 AND salary <= 800 THEN '3'
WHEN salary > 800 AND salary <= 1000 THEN '4'
ELSE NULL END;
3.關於IF-THEN-ELSE的其他完成
3.1 DECODE() 函數
select decode(sex, 'M', 'Male', 'F', 'Female', 'Unknown')
from employees;
貌似只要Oracle供給該函數，並且不支撐ANSI SQL，語法上也沒CASE WHEN清楚，小我不推舉應用。
3.2 在WHERE中特別完成
SELECT T2.*, T1.*
FROM T1, T2
WHERE (T2.COMPARE_TYPE = 'A' AND T1.SOME_TYPE LIKE 'NOTHING%')
OR
(T2.COMPARE_TYPE != 'A' AND T1.SOME_TYPE NOT LIKE 'NOTHING%')
這類辦法也是在特別情形下應用，要多留意邏輯，不要弄錯。
