php - 从其他表中选择具有条件规则(计数)的数据

Question

我的数据库中有这些结构:

Table coupon
coupon_id , code, max_used

Table coupon_history
coupon_history_id, coupon_id, used_date

我能否获取“coupon.max_used”不超过“coupon_history”总历史记录的优惠券数据？ 我被困在这里了。我需要一个 coupon_code。请帮助我。

Answer 1

尝试像这样使用 JOIN 和 IN:

SELECT cc.* FROM coupon cc
WHERE cc.coupon_id IN
  (
    SELECT c.coupon_id FROM Coupon c
    LEFT JOIN
    (  SELECT coupon_id, COUNT(coupon_id) maxUsed
         FROM coupon_history GROUP BY coupon_id
    ) ch 
    ON c.Coupon_id = ch.Coupon_id
    WHERE c.max_used > ch.maxUsed
       OR ch.maxUsed IS NULL
  );

或者您可以像这样简单地使用JOIN:

SELECT cc.* FROM coupon cc
JOIN 
  (
    SELECT c.coupon_id FROM Coupon c
    LEFT JOIN
    (  SELECT coupon_id, COUNT(coupon_id) maxUsed
         FROM coupon_history GROUP BY coupon_id
    ) ch 
    ON c.Coupon_id = ch.Coupon_id
    WHERE c.max_used > ch.maxUsed
       OR ch.maxUsed IS NULL
  ) c ON cc.coupon_id = c.coupon_id;

看看this SQLFiddle demo

---

编辑:关于你的second requirement

试试这个查询:

SELECT cc.*,c.TotalUsed FROM coupon cc
JOIN 
  (
    SELECT c.coupon_id,TotalUsed FROM Coupon c
    LEFT JOIN
    (  SELECT coupon_id, COUNT(coupon_id) TotalUsed
         FROM coupon_history GROUP BY coupon_id
    ) ch 
    ON c.Coupon_id = ch.Coupon_id
    WHERE c.max_used > ch.TotalUsed
       OR ch.TotalUsed IS NULL
  ) c ON cc.coupon_id = c.coupon_id;

参见this SQLFiddle