php 这是怎么回事呀

Question

 $sql=mysql_query("select usernc from tb_user where usernc='".$usernc."'",$conn);
 $info=mysql_fetch_array($sql);
 sql语句的问题

Answer 1

$sql=mysql_query("select usernc from tb_user where usernc=".$usernc,$conn);

Answer 2

conn代码
<?php
$conn=mysql_connect("localhost","root","root");
mysql_select_db("db_bcty365",$conn);
mysql_query("set names gb2312");
?>

Answer 3

$conn=mysql_pConnect("localhost","root","root");
mysql_select_db("db_bcty365");