left join
hr_salary.emp_id = earning_tax.emp_id (+)
--->
hr_salary left join earning_tax on hr_salary .emp_id = earning_tax.emp_id
hr_salary.emp_id = earning_tax.emp_id (+)
--->
hr_salary left join earning_tax on hr_salary .emp_id = earning_tax.emp_id
用户表user
user_id user_name skill_id
1 A 1
2 B 2
3 C
技能表skill
skill_id skill_name
1 打字
2 交际select
user.user_id,user.user_name,skill.skill_name
from
user,skill
where
user.skill_id=skill.skill_id(+)
1 A 打字
2 B 交际
3 C
sql server oracle
a *= b <=> a = b(+) 左连接
a =* b <=> a (+)= b 右连接当然也可以用 left join等。