php出现Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result

php出现Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result
<?php
$link= mysql_connect("localhost","root","root")or die("数据库连接失败".mysql_error());
mysql_select_db("student",$link);
mysql_query("set names gb2312");
?>
<?php
  $sql=mysql_query("select * ftom tb_student");
  $info=mysql_fetch_array("$sql");
  if($_POST[submit]=="查询")
  {
$tex_book=$_POST[tex_book];
$sql=mysql_query("select * ftom tb_student where sno like '%''.trim($tex_book).''%'");
$info=mysql_fetch_array($sql);
 
}
?>
<?php

[解决办法]
$info=mysql_fetch_array("$sql");
=>
$info=mysql_fetch_array($sql);

这里不要加引号。


另外确保select * ftom tb_student这条sql能成功执行。