可能重复:
SQL 查询如何有两个 from 子句?
delete from machine_placement_group
from (machine_group g
left join config_chg_req r
on g.machine_group_id = r.machine_group_id)
join machine_placement_group mg
on g.machine_group_id = mg.machine_group_id
我不明白这两个陈述。