[英]Join two fields from same table in mysql
SELECT pms.id,
pms.id_from,
pms.id_to,
pms.fecha,
pms.leida,
usuarios.img_src as avatar_from,
usuarios.alias as name_from,
usuarios.img_src as avatar_to,
usuarios.alias as name_to
FROM pms
LEFT JOIN usuarios ON usuarios.id = pms.id_from
LEFT JOIN usuarios ON usuarios.id = pms.id_to
The problem that is two references of usuario (alias or img_src) per row: 每行有两个引用用法(别名或img_src)的问题:
And I get this error: 我得到这个错误:
The following errors were reported:
Not unique table/alias: 'usuarios'
Or this 或这个
SELECT pms.id,
pms.id_from,
pms.id_to,
pms.fecha,
pms.leida,
usuarios.img_src as avatar_from,
usuarios.alias as name_from,
usuarios.img_src as avatar_to,
usuarios.alias as name_to
FROM pms
LEFT JOIN usuarios ON usuarios.id = pms.id_from OR usuarios.id = pms.id_to
Works, but I get same name and image for each _to and _from 可行,但每个_to和_from的名称和图像都相同
So, what's the way to go here? 那么,去这里的路是什么?
Yes joining the same table will require unique alias for the table name something as 是的,加入同一个表将需要唯一的别名来表示表名,例如
select
p.id,
p.id_from,
p.id_to,
p.fecha,
p.leida,
u1.img_src as avatar_from,
u1.alias as name_from,
u2.img_src as avatar_to,
u2.alias as name_to
from pms p
LEFT JOIN usuarios u1 ON u1.id = p.id_from
LEFT JOIN usuarios u2 ON u2.id = p.id_to
If you use the same table twice you need different alias names 如果您两次使用同一张表,则需要使用不同的别名
SELECT pms.id,
pms.id_from,
pms.id_to,
pms.fecha,
pms.leida,
u_from.img_src as avatar_from,
u_from.alias as name_from,
u_to.img_src as avatar_to,
u_to.alias as name_to
FROM pms
LEFT JOIN usuarios u_from ON u_from.id = pms.id_from
LEFT JOIN usuarios u_to ON u_to.id = pms.id_to
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