PHP can not modify the data to solve the idea

PHP Cannot modify data
I'm just a beginner PHP, I hope you teachers ask



if ($_get["type"]== "modify") {

$id =$_get[' id '];
if ($_post["SUBMIT3"])
{
$sql = "Update t_user set f_username= ' $a ', f_sex= ' $b ', f_age= ' $c ', f_ct= ' $d ', f_zaoyingji= ' $f ', f_buwei= ' $g ', f_hu= ' $h ', F _jishu= ' $i ', f_xiaoaguo= ' $j ', f_qianming= ' $k ', f_yanchi_time= ' $l ', f_chufa_time= ' $m ' where id= $id ';
mysql_query ($sql);
echo "";
}
$sql = "SELECT * from T_user where id= $id";
$rs =mysql_query ($sql);
$ros =mysql_fetch_row ($RS);
?>
$result = $connection->query ("select * from T_user where id= $id limit 1");
while ($rws = $result->fetch_row ()) {
?>
}
?>

------Solution--------------------
$rs =mysql_query ($sql) or Die (Mysql_error ()); It's a mistake to change the sentence into this way.
------Solution--------------------
PHP said you did not select the database, that is, you did not select the database!
------Solution--------------------
mysql_select_db () How is this set?
------Solution--------------------
You use mysqli to connect to the database
But with mysql_query ($sql); manipulating databases
What can I do with this whole thing?

Although MySQL extensions and mysqli extensions are used to manipulate MySQL databases
But they are two different sets of things that can't be mixed!

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