无法编写SQL查询

Question

我有一个限制表，其中存储着coupon_id，restriction_value和restriction_type。

coupon_id     restriction_value     restriction_type
-----------------------------------------
1             delhi                 city
2             delhi                 city
1             india                 country

我想返回一个查询，该查询为我提供适用于印度国家和德里城市的优惠券。

Answer 1

分别查询每个条件，并验证是否存在相同的优惠券ID：

SELECT DISTINCT a.coupon_id
FROM tableA a
JOIN (SELECT coupon_id FROM tableA WHERE restriction_value = 'delhi' AND restriction_type = 'city') b ON b.coupon_id = a.coupon_id
JOIN (SELECT coupon_id FROM tableA WHERE restriction_value = 'india' AND restriction_type = 'country') c ON c.coupon_id = a.coupon_id
WHERE b.coupon_id = c.coupon_id

Answer 2

选择城市“ delhi”的优惠券，该城市存在带有国家“印度”的记录。
像这样：

SELECT city.*
FROM   my_table city
WHERE  city.restriction_type = 'city'
  AND  city.restriction_value = 'delhi'
  AND  EXISTS (SELECT *
               FROM   my_table country
               WHERE  city.coupon_id = country.coupon_id
                 AND  country.restriction_type = 'country'
                 AND  country.restriction_value = 'india');

Answer 3

您可以编写如下的子查询。

SELECT
*
FROM coupon_table
where id in (
      select coupon_id 
      from restriction_table
      where (restriction_value = 'Delhi' AND restriction_type = 'city')
            OR (restriction_value = 'India' AND restriction_type = 'country')
);