关于数据库内连接外连接左连接右连接
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关于数据库内连接外连接左连接右连接
申明:此为网络转载,只为学习
数据库内连接、外连接(左连接、右连接)、全连接
内连接:把两个表中数据对应的数据查出来
外连接:以某个表为基础把对应数据查出来
外连接:以某个表为基础把对应数据查出来
全连接是以多个表为基础
student表
no name
1 a
2 b
3 c
4 d
grade表
no grade
1 90
2 98
3 95
内连接 inner join(查找条件中对应的数据,no4没有数据不列出来)
语法:select * from student inner join grade on student.no = grade.no
结果
student.no name grade.no grade
1 a 1 90
2 b 2 98
3 c 3 95
左连接(左表中所有数据,右表中对应数据)
语法:select * from student left join grade on student.no = grade.no
结果:
student.no name grade.no grade
1 a 1 90
2 b 2 98
3 c 3 95
4 d
右连接(右表中所有数据,左表中对应数据)
语法:select * from student right join grade on student.no = grade.no
结果:
student.no name grade.no grade
1 a 1 90
2 b 2 98
3 c 3 95
全连接
语法:select * from student full join grade on student.no = grade.no
结果:
no name grade
1 a 90
2 b 98
3 c 95
4 d
1 a 90
2 b 98
3 c 95
student表
no name
1 a
2 b
3 c
4 d
grade表
no grade
1 90
2 98
3 95
内连接 inner join(查找条件中对应的数据,no4没有数据不列出来)
语法:select * from student inner join grade on student.no = grade.no
结果
student.no name grade.no grade
1 a 1 90
2 b 2 98
3 c 3 95
左连接(左表中所有数据,右表中对应数据)
语法:select * from student left join grade on student.no = grade.no
结果:
student.no name grade.no grade
1 a 1 90
2 b 2 98
3 c 3 95
4 d
右连接(右表中所有数据,左表中对应数据)
语法:select * from student right join grade on student.no = grade.no
结果:
student.no name grade.no grade
1 a 1 90
2 b 2 98
3 c 3 95
全连接
语法:select * from student full join grade on student.no = grade.no
结果:
no name grade
1 a 90
2 b 98
3 c 95
4 d
1 a 90
2 b 98
3 c 95