请问一下php的pdo如何插入一个新字段？谢谢了！

$config = [

'user' =>'root',

'passwd' =>'root',

]

try {

$db = new PDO('mysql:host=172.17.0.1port=3306dbname=test', $config['user'], $config['passwd'])

# 新建一张表 A

$db->exec('create table if not exists A (

id int unsigned not null primary key auto_increment comment \'主键id\'

)')

# 给表 A 新增一个字段 name

$db->exec('alter table A add column name varchar(50) not NULL default \'\' comment \'名称\'')

} catch (PODException $e) {

print("Error: " . $e->getMessage())

exit()

}

class MysqlManage{

/*创建数据库，并且主键是aid

* table 要查询的表名

*/

function createTable($table){

$sql="CREATE TABLE IF NOT EXISTS `$table` (`aid` INT NOT NULL primary key)ENGINE = InnoDB"

M()->execute($sql)

$this->checkTable($table)

}

/*

* 检测表是否存在，也可以获取表中所有字段的信息

* table 要查询的表名

* return 表里所有字段的信息

*/

function checkTable($table){

$sql="desc `$table`"

$info=M()->execute($sql)

return $info

}

/*

* 检测字段是否存在，也可以获取字段信息(只能是一个字段)

* table 表名

* field 字段名

*/

function checkField($table,$field){

$sql='desc `$table` $field'

$info=M()->execute($sql)

return $info

}

/*

* 添加字段

* table 表名

* info 字段信息数组 array

* return 字段信息 array

*/

function addField($table,$info){

$sql="alter table `$table` add column"

$sql.=$this->filterFieldInfo()

M()->execute($sql)

$this->checkField($table,$info['name'])

}

/*

* 修改字段

* 不能修改字段名称，只能修改

*/

function editField($table,$info){

$sql="alter table `$table` modify "

$sql.=$this->filterFieldInfo($info)

M()->execute($sql)

$this->checkField($table,$info['name'])

}

/*

* 字段信息数组处理，供添加更新字段时候使用

* info[name] 字段名称

* info[type] 字段类型

* info[length] 字段长度

* info[isNull] 是否为空

* info['default'] 字段默认值

* info['comment'] 字段备注

*/

private function filterFieldInfo($info){

if(!is_array($info))

return

$newInfo=array()

$newInfo['name']=$info['name']

$newInfo['type']=$info['type']

switch($info['type']){

case 'varchar':

case 'char':

$newInfo['length']=empty($info['length'])?100:$info['length']

$newInfo['isNull']=$info['isNull']==1?'NULL':'NOT NULL'

$newInfo['default']=empty($info['default'])?'':'DEFAULT '.$info['default']

$newInfo['comment']=empty($info['comment'])?'':'COMMENT '.$info['comment']

break

case 'int':

$newInfo['length']=empty($info['length'])?7:$info['length']

$newInfo['isNull']=$info['isNull']==1?'NULL':'NOT NULL'

$newInfo['default']=empty($info['default'])?'':'DEFAULT '.$info['default']

$newInfo['comment']=empty($info['comment'])?'':'COMMENT '.$info['comment']

break

case 'text':

$newInfo['length']=''

$newInfo['isNull']=$info['isNull']==1?'NULL':'NOT NULL'

$newInfo['default']=''

$newInfo['comment']=empty($info['comment'])?'':'COMMENT '.$info['comment']

break

}

$sql=$newInfo['name']." ".$newInfo['type']

$sql.=(!empty($newInfo['length']))?($newInfo['length']) .' ':' '

$sql.=$newInfo['isNull'].' '

$sql.=$newInfo['default']

$sql.=$newInfo['comment']

return $sql

}

/*

* 删除字段

* 如果返回了字段信息则说明删除失败，返回false，则为删除成功

*/

function dropField($table,$field){

$sql="alter table `$table` drop column $field"

M()->execute($sql)

$this->checkField($table,$filed)

}

/*

* 获取指定表中指定字段的信息(多字段)

*/

function getFieldInfo($table,$field){

$info=array()

if(is_string($field)){

$this->checkField($table,$field)

}else{

foreach($field as $v){

$info[$v]=$this->checkField($table,$v)

}

}

return $info

}

}