表連接多個group_concat

Question

我有關於與group_concat連接表的問題。這裏是細節。

table_orders：

item_cd order_id descs   quantity status seq_no 
1   100  coca-cola   2   A   232 
2   100  pizza    1   A   233 
3   101  cheeseburger  5   A   234 
4   102  pepsi    4   A   235 
4   

table_instructions：

item_cd instruction 
    3   more cheese 
    3   less vegetable 

cancelled_item_table：

quantity seq_no 
    1  234 
    1  234 
    1  235 

現在我要實現的是這樣的：

item_cd descs   quantity instructions     cancelled_item 
1   coca-cola   2  -         - 
2   pizza    1  -         - 
3   cheeseburger  2  more cheese, less vegetable  1,1 
4   pepsi    4  -         1 

這是我當前的查詢：

SELECT 
    ord.item_cd, 
    ord.order_id, 
    ord.descs, 
    ord.quantity, 
    GROUP_CONCAT(x.quantity) as cancelled, 
    GROUP_CONCAT(i.instruction) as instruct 
FROM table_orders ord 
LEFT JOIN cancelled_item_table x ON ord.seq_no = x.seq_no 
LEFT JOIN table_instructions i ON ord.item_cd = i.item_cd  
WHERE ord.status = 'A' 
GROUP BY ord.order_id 

這裏是輸出：

item_cd descs   quantity instructions     cancelled_item 
1   coca-cola   2  -         1 
2   pizza    1  -         1 
3   cheeseburger  2  more cheese, more cheese, 
            less vegetable, less vegetable 1,1,1,1 
4   pepsi    4  -         1 

如果你注意到，吉士漢堡有2個取消的項目和2個指令，但輸出爲4，外觀喜歡它的倍增。

Answer 1

由於與cancelled_item_table乘行加入，你必須加入一個已經分組子查詢，像這樣：

SELECT 
    ord.item_cd, 
    ord.order_id, 
    ord.descs, 
    ord.quantity - coalesce(x.tot,0) as quantity, 
    GROUP_CONCAT(i.instruction) as instruct, 
    x.cancelled 
FROM 
    table_orders ord LEFT JOIN table_instructions i 
    ON ord.item_cd = i.item_cd LEFT JOIN 
    (select seq_no, count(*) as tot, GROUP_CONCAT(quantity) as cancelled 
    from cancelled_item_table 
    group by seq_no) x ON ord.seq_no = x.seq_no 
WHERE ord.status = 'A' 
GROUP BY ord.item_cd, ord.order_id, ord.descs, quantity