Question

我有两个表user和product具有一对多关系（一个user可能有多个product）。

我想创建一个查询以获取所有同时具有橙和香蕉的user。在下面的示例中，这将是john和leeroy。

如何制定查询条件？

只有一种情况，我会变成：

SELECT * FROM "user" 
INNER JOIN "product" ON "product"."fk_user" = "user"."id"
WHERE "product"."product" = 'banana';

user表

╔════╦═════════╗
║ id ║ name    ║
╠════╬═════════╣
║ 1  ║ michael ║
╠════╬═════════╣
║ 2  ║ john    ║
╠════╬═════════╣
║ 3  ║ leeroy  ║
╠════╬═════════╣
║ 4  ║ tony    ║
╚════╩═════════╝

product表

╔═════════╦═════════╗
║ product ║ fk_user ║
╠═════════╬═════════╣
║ orange  ║ 1       ║
╠═════════╬═════════╣
║ orange  ║ 2       ║
╠═════════╬═════════╣
║ banana  ║ 2       ║
╠═════════╬═════════╣
║ banana  ║ 3       ║
╠═════════╬═════════╣
║ orange  ║ 3       ║
╠═════════╬═════════╣
║ banana  ║ 4       ║
╚═════════╩═════════╝

Answer 1

您可以使用两个联接：

SELECT u.* 
FROM user u
INNER JOIN product p1
ON p1.fk_user=u.id
AND p1.product='banana'
INNER JOIN product p2
ON p2.fk_user=u.id
AND p2.product='orange'

Answer 2

按用户分组并使用agateway: cl_profile: "sl6.5-x86_64" prefix: "aicgateway" primary_role: "STANDARDV3" requires_pool: false ac-edge: cl_profile: "sl6.5-x86_64" prefix: "ac-edge" primary_role: "STANDARDV3" requires_pool: false webnode: cl_profile: "centos-5.6-x86_64-db-v2" vlans: ["frontend"] label: "Frontend" prefix: "web" primary_role: "FRONTEND" requires_pool: false检查用户的产品。

HAVING

编辑：我应该补充一点，有几种方法可以编写这种子查询。一个select * from user where id in ( select fk_user from product group by fk_user having count(case when product = 'orange' then 1 end) > 0 and count(case when product = 'banana' then 1 end) > 0 );子句可以加快速度，使用这样的子句，您可以只计算发现的不同产品：

WHERE

Answer 3

最直接的声明（IMHO）将使用两个IN子句：

select *
from user
where id in
(
  select fk_user
  from product
  WHERE product = 'orange')
and id in
(
  select fk_user
  from product
  WHERE product = 'banana')

Answer 4

If you just want the user id and not the name, you can use aggregation:

SELECT p.fk_user
FROM product p
WHERE p.product in ('banana', 'orange')
GROUP BY p.fk_user
HAVING COUNT(*) FILTER (WHERE p.product = 'banana') > 0 AND
       COUNT(*) FILTER (WHERE p.product = 'orange') > 0;

If you need additional columns from user as well, I would go with the IN version suggested by DStanley, although I would use EXISTS rather than IN.

Answer 5

这是relational-division的情况。
如果（就像典型情况一样，您的示例数据似乎也支持）...

您需要的只是用户ID
存在FOREIGN KEY约束，用于强制引用完整性
以及对UNIQUE的{{1}}约束-（对于我的查询，隐含providing the perfect index）

..然后它就快了：

product(product, fk_user)

我们在这里收集了大量基础技术：

How to filter SQL results in a has-many-through relation

最佳选择取决于缺少的规格-以及个人偏好。

此外：user是一个保留字，请勿将其用作表名。

INNER JOIN中的多个条件

5 个答案: