[英]Optimize complicated SQL query
抱歉,如果这很明显,但我对SQL并不擅长。 我有几个表都需要连接,但其中一个列可以为null。
我有这个问题:
select orders.ordnum, orders.tstamp, orders.sku, code, redeemed_order_num, null as redeemed_date, null as fullname
from customer_subscriptions orders
join bulk_codes codes
on codes.bulk_order_id = orders.subscription_id
where (orders.sku="bulk-box" or orders.sku="bulk-book") and redeemed_order_num is null
union
select orders.ordnum, orders.tstamp, orders.sku, code, redeemed_order_num, redeemed_orders.date redeemed_date, customers.fullname
from customer_subscriptions orders
join bulk_codes codes
on codes.bulk_order_id = orders.subscription_id
join customer_subscriptions redeemed_orders
on codes.redeemed_order_num = redeemed_orders.ordnum
join customers
on customers.cid = redeemed_orders.cid
where (orders.sku="bulk-box" or orders.sku="bulk-book")
顶部选择返回前9行,底部返回一行。
有什么方法可以优化吗?
完整的架构在这里: https : //pastebin.com/FXGLetcV
我想你只需要left join
:
SELECT orders.ordnum, orders.tstamp, orders.sku, code,
redeemed_order_num, redeemed_orders.date redeemed_date, customers.fullname
FROM customer_subscriptions orders JOIN
bulk_codes codes
ON codes.bulk_order_id = orders.subscription_id LEFT JOIN
customer_subscriptions redeemed_orders
ON codes.redeemed_order_num = redeemed_orders.ordnum LEFT JOIN
customers
ON customers.cid = redeemed_orders.cid
WHERE orders.sku IN ('bulk-box', 'bulk-book')
以下是查询。
Select orders.ordnum, orders.tstamp, orders.sku, code, redeemed_order_num, null as redeemed_date, null as fullname
From customer_subscriptions orders
Inner join bulk_codes codes
On codes.bulk_order_id = orders.subscription_id
And redeemed_order_num is null -- comment
Left outer join bulk_codes codes
On codes.bulk_order_id = orders.subscription_id
left outer join customer_subscriptions redeemed_orders
On COALESCE(codes.redeemed_order_num, 111111) = redeemed_orders.ordnum
left outer join customers
On customers.cid = redeemed_orders.cid
where orders.sku='bulk-box'
Or orders.sku='bulk-book'
在您给出的查询中,首先选择仅加入具有空值的redeemed_order_num,并且在第二个选择中加入redeemed_order_num,使用coalesce或IFNULL函数替换连接条件中的空值
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