使用查询语句select,进行列的查询,例如username列,select * from test;查询全部数据,select username from test;查询username列,现在给username进行一个命名,select username as '姓名' from test;现在给特定的列限定条件,select username as '姓名' from test where id < 3;这个小于符号可以改写为大于等于,当然也可以限制查询几条数据,select username as '姓名' from test where id <3,这里是查询一条数据,当然也可以查询在某个区间,使用的是between and的使用select username as '姓名' from test where id between 2 and 3 limit 4;