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[英]Alternative to GROUP_CONCAT? Multiple joins to same table, different columns
[英]table joins with multiple group_concat
關於使用group_concat連接表有問題。 這是詳細信息。
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
現在我想要實現的是這樣的:
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
這是我目前的查詢:
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,芝士漢堡有2個取消的項目和2個指令,但輸出是4,看起來它正在成倍增加。
由於使用cancelled_item_table
的連接將行相乘,您必須加入已經分組的子查詢,如下所示:
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
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