T-SQL - 錯誤上Case語句

Question

USE NORTHWIND; 
GO 
SELECT SHIPCOUNTRY,[ORDERS_ID] = 
CASE ORDERID 
WHEN ORDERID = 10300 
THEN 'I AM FROM 10300' 
WHEN ORDERID = 10400 
THEN 'I AM FROM 10400' 
WHEN ORDERID = 10500 
THEN 'I AM FROM 10500' 
ELSE 'I AM OUT OF RANGE' 
END 
FROM ORDERS; 
GO 

錯誤 - 消息102，級別15，狀態1，行3附近有語法錯誤 '='。

如果你在你的sql server中有Northwind Database，你可以執行這個查詢。

我不明白問題在哪裏。任何人都可以幫我解決這個問題嗎？

Answer 1

試試這個：

USE NORTHWIND; 
GO 
SELECT SHIPCOUNTRY, 
CASE ORDERID 
WHEN 10300 
THEN 'I AM FROM 10300' 
WHEN 10400 
THEN 'I AM FROM 10400' 
WHEN 10500 
THEN 'I AM FROM 10500' 
ELSE 'I AM OUT OF RANGE' 
END as OrdersId 
FROM ORDERS; 
GO 

當您在初始CASE xxxx聲明是明確的，你不能重複的變量在WHEN條款。這同樣適用：

USE NORTHWIND; 
GO 
SELECT SHIPCOUNTRY, 
CASE 
WHEN ORDERID = 10300 
THEN 'I AM FROM 10300' 
WHEN ORDERID = 10400 
THEN 'I AM FROM 10400' 
WHEN ORDERID = 10500 
THEN 'I AM FROM 10500' 
ELSE 'I AM OUT OF RANGE' 
END as OrdersId 
FROM ORDERS; 
GO 

您也不能指定這樣的別名。在CASE塊之後使用AS關鍵字。

編輯：根據亞當溫格的評論，你確實可以在你的查詢中寫入別名[alias] = fieldname。感謝您的更正！

Answer 2

USE NORTHWIND; 
GO 
SELECT SHIPCOUNTRY, 
CASE ORDERID 
WHEN 10300 
THEN 'I AM FROM 10300' 
WHEN 10400 
THEN 'I AM FROM 10400' 
WHEN 10500 
THEN 'I AM FROM 10500' 
ELSE 'I AM OUT OF RANGE' 
END as [ORDERS_ID] 
FROM ORDERS; 
GO 

Answer 3

USE NORTHWIND; 
GO 
SELECT SHIPCOUNTRY, 
CASE ORDERID 
    WHEN 10300 
    THEN 'I AM FROM 10300' 
    WHEN 10400 
    THEN 'I AM FROM 10400' 
    WHEN 10500 
    THEN 'I AM FROM 10500' 
    ELSE 'I AM OUT OF RANGE' 
END ORDERS_ID 
FROM ORDERS; 
GO 

Answer 4

CASE帶有兩種格式：簡單和搜索。你在混合它們。

http://msdn.microsoft.com/en-us/library/ms181765.aspx

Answer 5

的case結構可以有兩種不同的形式：

case n 
    when n then n 
    when n then n 
end 

和：

case 
    when n = n then n 
    when n = n then n 
end 

你將它們混合。使用：

SELECT SHIPCOUNTRY,[ORDERS_ID] = 
    CASE ORDERID 
    WHEN 10300 THEN 'I AM FROM 10300' 
    WHEN 10400 THEN 'I AM FROM 10400' 
    WHEN 10500 THEN 'I AM FROM 10500' 
    ELSE 'I AM OUT OF RANGE' 
    END 
FROM ORDERS