Question

大家好，我有那个SQL：

SELECT p.* FROM products p WHERE required_product_id IS NULL 
UNION ALL
SELECT  p.* FROM products p, orders o WHERE p.required_product_id = o.product_id 
AND o.user_id = 1
UNION DISTINCT
SELECT p.`*` FROM products p, orders o WHERE p.id NOT IN (SELECT product_id FROM orders WHERE product_id = p.id AND o.user_id = 1)
AND p.max_buys = 1;

此查询首先检查是否购买了商品并显示下一个商品！我想检查用户是否购买了该产品，以仅退还该用户未购买的产品

表结构=产品：http://prntscr.com/k6ogp4，订单：http://prntscr.com/k6ogrz

max_buys列于产品上（如果为1，则可以购买一次；如果为0，则可以多次购买）

Answer 1

在您的情况下，我希望有一个灵活的查询来管理需求，并且我认为在这种情况下[如果您的描述完整]则不需要UNION。

SELECT w.* from (
  SELECT 
    (SELECT count(o.product_id) FROM orders o WHERE o.product_id = p.id AND o.user_id = 1) bought_count,
    (SELECT count(q.product_id) FROM orders q WHERE q.product_id = p.required_product_id AND q.user_id = 1)  order_depend,
    p.* 
  FROM products p  ) w
where 
  (order_depend>0 or required_product_id is null) and -- unlock order depended products
  (max_buys=0 or   -- can buy more than once
  bought_count=0)  -- or not bought yet
order by 
    order_depend desc, -- dependent products to ordered products in first level
    bought_count asc,  -- not bought products in second level
    recommended desc   -- recommended products in third level

您还可以根据需要管理其他任何订单。

MySQL UNION，检查其是否为粗体

1 个答案: