node 操作mysql，为什么查询字符串里面有的用反引号``,有的用双引号""呢，是有什么意义吗,希望解答疑惑

//查询
var selectSQL='select * from `mytable`';
//添加
var insertSQL='insert into `mytable` (`name`)values("mary")';
//修改
var updateSQL='update `mytable` set `name`="caton" where name="mary"'
//删除
var deleteSQL='delete from `mytable` where `name` like "caton"';

//执行SQL
connection.query(updateSQL, function(err, rows) {
    if (err) throw err;
});