MYSQL CASE問題

Question

我有一個表格存儲買家和供應商之間的交易，交易按表示信用票據或發票的「doctype」分類。我正嘗試創建一個視圖，顯示相同交易的類似邊界的視圖。

SELECT 
SUM(CASE doctype WHEN doctype = 1 THEN docvalue END) AS Invoice, 
SUM(CASE doctype WHEN doctype = 2 THEN docvalue END) AS CreditNote, 
SUM(CASE doctype WHEN doctype = 3 THEN docvalue END) AS JournalEntry, 
SUM(CASE doctype WHEN doctype = 4 THEN docvalue END) AS Payment 
FROM transactions 
group by buyer 

當我運行此查詢時，我看到第一個CASE語句的結果，但其餘的返回空值。有一個更好的方法嗎？

我的目標是將此作爲視圖，但我甚至無法獲得查詢以顯示我想要的內容。我也嘗試過下面的一個可怕的黑客，但它甚至不工作

SELECT 
(sum(docvalue) 
    FROM transactions where doctype =1) as invoices, 
(sum(docvalue) 
    FROM transactions where doctype =2) as creditnotes, 
(sum(docvalue) 
    FROM transactions where doctype =3) as journals, 
(sum(docvalue) 
    FROM transactions where doctype =4) as payments 
from transactions 

我會把我的頭髮掉，但我是禿頭！

Answer 1

CASE的語法不正確。這裏是一個修改版本：

SELECT 
SUM(CASE doctype WHEN 1 THEN docvalue END) AS Invoice, 
SUM(CASE doctype WHEN 2 THEN docvalue END) AS CreditNote, 
SUM(CASE doctype WHEN 3 THEN docvalue END) AS JournalEntry, 
SUM(CASE doctype WHEN 4 THEN docvalue END) AS Payment 
FROM transactions 
group by buyer