Require instructions to fill in the same fields into multiple tables

Fill in records with the same fields in multiple tables for guidance
Why is this wrong?

$username = $_post[' username ');
$password = $_post[' psd '];
$sex = $_post[' sex '];
$grade = $_post[' grade ');
$age = $_post[' age '];
$height =$_post[' height '];
$weight =$_post[' weight '];

Check form data
if (!preg_match ('/^[\w\x80-\xff]{3,15}$/', $username)) {
Exit (' ERROR: User name does not meet requirements!back ');
}
if (strlen ($password) < 6) {
Exit (' ERROR: Password length does not meet requirements!back ');
}


Include (' conn.php ');


$sql = "INSERT into user (username,password,sex,grade,age,height,weight) VALUES (' $username ', ' $password ', ' $sex ', ' $ Grade ', ' $age ', ' $height ', ' $weight ');
INSERT into Module1 (username) VALUES (' $username ');
INSERT into Module2 (username) VALUES (' $username ');
INSERT into Module3 (username) VALUES (' $username ');
INSERT into Module4 (username) VALUES (' $username ');
INSERT into Module5 (username) VALUES (' $username ');
if (mysql_query ($sql, $conn))
Exit (' Register successfully! Click here to log in ');
Else
Echo ' Sorry, registration Error!: ', mysql_error (), '
';
Echo ' Click here to return to retry ';

?>
------Solution--------------------
Oh, I just noticed you.
$sql. = ' INSERT into Module1 (username) VALUES (' $username '); '
$sql. = ' INSERT into Module2 (username) VALUES (' $username '); '
$sql. = ' INSERT into Module3 (username) VALUES (' $username '); '
$sql. = ' INSERT into module4 (username) VALUES (' $username '); '
$sql. = ' INSERT into module5 (username) VALUES (' $username '); '
Then use Mysqli::multi_query () to support multi-statement execution MySQL can only be a single statement execution, so you plug 5 times to perform 5 times mysql_query

