问题:我有一份姓名和地址列表.一些名称(人)与其他名称(人)具有相同的地址(街道、邮政编码、城镇).我想选择所有地址不超过三个的名称,其余的前三个名称中的每一个都指向同一个地址.示例:
Problem: I have a list of names and addresses. Some names (persons) have the same address (street, zip code, town) like others. I want to select all those names with addresses with no more than three occurrences and from the rest the first three names each of a bunch pointing to the same address. Example:
Albert | Adr1 Berta | Adr1 Cesar | Adr1 Donald | Adr1 Eric | Adr2 Fritz | Adr2 Gerd | Adr2 Henry | Adr3结果集应该是
Albert | Adr1 Berta | Adr1 Cesar | Adr1 Eric | Adr2 Fritz | Adr2 Gerd | Adr2 Henry | Adr3Donald 失踪了,因为他是同一个地址组中的第四个.这个结果可以用 UNION 和子查询来实现吗?类似的东西
Donald is missing because he is the 4th of a group with the same address. Can this result be achieved with UNIONs and subqueries? Something like
select * from addresses where address in (select address from addresses group by address having count(address) <= 3) UNION select * from addresses where address in (select address from addresses group by address having count(address) > 3 limit 3)我知道这个查询是错误的,因为它限制了超过 3 次出现的地址的完整结果集.我想知道这是否可以在带有 UNION 和子查询的单个 SELECT 中完成.我现在将在程序上使用 PHP/MySQL 来完成,但只是为了好玩,我会对仅 SQL 的解决方案感兴趣.
I know that this query is wrong because it limits the complete result set of addresses with more than 3 occurences. I wonder if this can be done in a single SELECT with UNIONs and subqueries. I will do it now procedurally with PHP/MySQL, but just for fun would be interested in an SQL only solution.
我查看了 SQL 查询,其中限制了一个表中的行,而不是结果集,但这并不反映我的情况 - 是吗?
I had a look at SQL query with limit on rows from one table, not the result set, but this does not reflect my situation - or does it?
推荐答案你可以试试类似
SELECT PersonName, Address FROM ( SELECT *, (SELECT COUNT(1) FROM addresses WHERE Address = a.Address AND PersonName < a.PersonName) CountLess FROM addresses a ) sub WHERE sub.CountLess <= 2更多推荐
如何将 SQL 结果集限制为不太常见的项目
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