mysql数据查询问题

PHP code:


$query=mysql_query("select * from yonghu_t where yonghu_yhmm=$addusername");
if($query){
echo "<script>";
echo "alert(‘用户名已经存在’); window.history.go(-1);";
echo "</script>";
}else{

$sql="insert into yonghu_t (yonghu_yhmc,yonghu_yhmm,yonghu_yhsf,yonghu_lxfs,yonghu_yx,yonghu_jdsj) values('$addusername','$password1','$yhsf','$lxfs','$addemail',$time)";
echo "<br>".$sql;
$return=mysql_query($sql);
}


意思就是先查询，数据里面没有再插入！可是我每次执行。都插入到数据库了，这是为什么呢？

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你的判断有问题

if($query)

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"select * from yonghu_t where yonghu_yhmm=\"".$addusername."\""

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"select * from yonghu_t where yonghu_yhmm=$addusername"====》"select * from yonghu_t where yonghu_yhmm='$addusername'"

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mysql_query 的返回值 false不是查不到数据，而是你的sql语句有错误。
判断有没有，你可以写个sql语句
$query=mysql_query("select count(*) from yonghu_t where yonghu_yhmm=$addusername");

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PHP code:

$sql = "se