避免在SQLJOIN上重复

您应该两次加入tableb，一次用于Plumber，另一次用于estimator

select a.ID,  a.ID_Name, b1.name plumber, b2.name estimator, a.amount
from tableA a
inner join tableb b1 on a.id = b1.id and b1.role ='Plumber'
inner join tableb b2 on a.id = b2.id and b2.role ='Estimator'

如果有重复的行，则应使用不同的行

select distinct  a.ID,  a.ID_Name, b1.name plumber, b2.name estimator, a.amount
from tableA a
inner join tableb b1 on a.id = b1.id and b1.role ='Plumber'
inner join tableb b2 on a.id = b2.id and b2.role ='Estimator'