mysql - SQL join 子句返回出现多次而不分组的行

Question

我想从 JOIN 查询中提取多次出现的记录，但没有将它们分组。

示例表：

tbl_names
id    Name
1     Mark
2     John
3     Jane
4     Paul

tbl_locations
id    Location
1     Berlin
2     Frankfurt
2     Stockholm
3     Helsinki
3     Madrid
3     London
4     Paris

ID 是外键。

现在，查询的结果将是：

id     Name    Location
2      John    Frankfurt
2      John    Stockholm
3      Jane    Helsinki
3      Jane    Madrid
3      Jane    London

即第一个表中的记录在JOIN子句结果中出现多次的所有JOIN记录。

我当然可以把它分组：

SELECT tbl_names.id, tbl_names.Name, tbl_locations.Location FROM tbl_names
 INNER JOIN tbl_locations ON (tbl_names.id = tbl_locations.id)
 GROUP BY tbl_names.id
 HAVING COUNT(tbl_names.id) > 1

我想要的是让它们根本不分组。我尝试过使用子条款，NOT IN但它非常慢并且没有给我想要的结果。

任何启蒙都会受到欢迎。

Answer 1

使用这个：

SELECT tbl_names.id, tbl_names.Name, tbl_locations.Location
FROM tbl_names
INNER JOIN tbl_locations ON (tbl_names.id = tbl_locations.id)
where tbl_names.id in (select id from tbl_locations
                       group by id having count(*) > 1);

此选择显示您已经拥有的连接，但仅选择名称/ID，它们在位置表中具有超过 1 个条目。

根据https://stackoverflow.com/a/3520552/1741542，这可能比普通子查询更快：

create view view_id_locations as
    select id
    from tbl_locations
    group by id
    having count(*) > 1;

SELECT tbl_names.id, tbl_names.Name, tbl_locations.Location
FROM tbl_names
INNER JOIN tbl_locations ON tbl_names.id = tbl_locations.id
inner join view_id_locations on tbl_names.id = view_id_locations.id;