求一条SQL语句：查询条件为字符前段相同从table1表中sel
从tae1表中select出a1列（字符型） 满足：a1中的数据满足前面的几个字符与变量ch相同 ch、a1的长度都不确定
asp:"select a1 from table1 where a1 like '" & ch & "%'" php:"select a1 from table1 where a1 like '" . $ch . "%'" 其他："select a1 from table1 where a1 like '"+ch+."%'"