mysql中的inner join,left join,right join
2017-07-19 12:45
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内连接 INNER JOIN,左连接 left join ,右连接 left join 是在查询数据用到多张表时会用的知识点 如果仅仅是对一张表中的数据进行查询就没法进行连接了
-- 内连接 INNER JOIN
语法: select * from 表1 INNER JOIN 表2 On 表1.ID=表2.ID (表1.ID,表2.ID之间要有关系)
例如:SELECT * from student st INNER JOIN score sc on st.id=sc.Stu_id
-- left join 左连接
语法: select * from 表1 left JOIN 表2 On 表1.ID=表2.ID (表1.ID,表2.ID之间要有关系)
例如:SELECT * from student st LEFT JOIN score sc ON st.id=sc.Stu_id
-- 右连接 right join
语法: select * from 表1 right JOIN 表2 On 表1.ID=表2.ID (表1.ID,表2.ID之间要有关系)
例如:SELECT * from student st RIGHT JOIN score sc ON st.id=sc.Stu_id
-- 内连接 INNER JOIN
语法: select * from 表1 INNER JOIN 表2 On 表1.ID=表2.ID (表1.ID,表2.ID之间要有关系)
例如:SELECT * from student st INNER JOIN score sc on st.id=sc.Stu_id
-- left join 左连接
语法: select * from 表1 left JOIN 表2 On 表1.ID=表2.ID (表1.ID,表2.ID之间要有关系)
例如:SELECT * from student st LEFT JOIN score sc ON st.id=sc.Stu_id
-- 右连接 right join
语法: select * from 表1 right JOIN 表2 On 表1.ID=表2.ID (表1.ID,表2.ID之间要有关系)
例如:SELECT * from student st RIGHT JOIN score sc ON st.id=sc.Stu_id
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