Mysql中on,in,as,where的区别
答:Where查询条件,on内外连接时候用,as作为别名,in查询某值是否在某条件里
创建2个表:student,score
student:
score:
where
SELECT * FROM student WHERE s_sex='男'
例如:on
SELECT * FROM student LEFT JOIN score on student.s_id=score.s_id;
on和where组合:
SELECT * FROM student LEFT JOIN score on student.s_id=score.s_id WHERE s_name='赵雷'
例如:in
SELECT * FROM score WHERE s_id in (SELECT s_id FROM student WHERE s_name='赵雷')
as
select * from score as a LEFT JOIN student as b on a.s_id=b.s_id where s_name='赵雷'