group_concat，GROUP BY和空值的月度值

Question

我試圖用group_concat在一年中輸出每個月的付款，即使沒有付款，而按類別分組。 amount是按月排列的每月總支付的逗號分隔列表。 從下面的查詢電流輸出是：

label  amount 
NULL  0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00 
Food  17.90,977.25 
Transport 40.00 

我不能管理合並與其他的空標籤以及沒有支出類別清單。我認爲這可能與我參加表格的方式有關？

預期的輸出結果是：

label  amount 
Healthcare 0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00 
Food  0.00,0.00,17.90,0.00,977.25,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00 
Transport 40.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00 

我當前的查詢是：

select label, group_concat(payment) as amount 
from(
SELECT 
categoryName as label, 
YEAR(t1.transactionDate), 
t.month, 
coalesce(SUM(t1.transactionAmount),0) payment 
FROM 
(SELECT 1 AS `month` 
UNION 
SELECT 2 AS `month` 
UNION 
SELECT 3 AS `month` 
UNION 
SELECT 4 AS `month` 
UNION 
SELECT 5 AS `month` 
UNION 
SELECT 6 AS `month` 
UNION 
SELECT 7 AS `month` 
UNION 
SELECT 8 AS `month` 
UNION 
    SELECT 9 AS `month` 
UNION 
    SELECT 10 AS `month` 
UNION 
    SELECT 11 AS `month` 
UNION 
SELECT 12 AS `month` 
) AS t 
LEFT JOIN transaction t1 on(t.month = MONTH(t1.transactionDate)) 
LEFT JOIN category USING (categoryID) 
where userid = 1 or userid is null group by t.month)a group by label 

任何幫助將是巨大的，因爲我一直是這樣摔跤有什麼進展了一會兒。 謝謝！

Answer 1

我認爲關鍵是在類別和月份上使用笛卡爾連接。我沒有測試過，但它必須接近解決方案：

select label, group_concat(monthly_sum separator ',') as amount 
from (
    select c.categoryName as label, coalesce(sum(t1.payment), 0) as monthly_sum 
    from category c 
    join (
     SELECT 1 AS month 
     UNION 
     SELECT 2 AS month 
     UNION 
     SELECT 3 AS month 
     UNION 
     SELECT 4 AS month 
     UNION 
     SELECT 5 AS month 
     UNION 
     SELECT 6 AS month 
     UNION 
     SELECT 7 AS month 
     UNION 
     SELECT 8 AS month 
     UNION 
     SELECT 9 AS month 
     UNION 
     SELECT 10 AS month 
     UNION 
     SELECT 11 AS month 
     UNION 
     SELECT 12 AS month 
    ) t 
    left join transaction t1 on t.month = MONTH(t1.transactionDate) 
    where userid = 1 or userid is null 
    group by t.month, c.categoryName 
) a 
group by label