MYSQL CASE问题

Question

我有一个表格存储买家和供应商之间的交易，交易按表示信用票据或发票的“doctype”分类。我正尝试创建一个视图，显示相同交易的类似边界的视图。

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 

当我运行此查询时，我看到第一个CASE语句的结果，但其余的返回空值。有一个更好的方法吗？

我的目标是将此作为视图，但我甚至无法获得查询以显示我想要的内容。我也尝试过下面的一个可怕的黑客，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 

我会把我的头发掉，但我是秃头！

Answer 1

CASE的语法不正确。这里是一个修改版本：

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