php & mysql please select an other date- message is not appearing - php

Question

I have two issues and both are linked. First, "already booked - please select another date" is not appearing, if two clients select the same product (pg_no) and date (Date). These fields are UNIQUE CONSTRAINT.
Second, when data is inserted or submitted localhost shows complete address
http://localhost/lstcomp/index.php?note=submitted. But when it fails the localhost shows only : http://localhost/lstcomp/
<?php
//connecting string
include("dbconnect.php");
//assigning
$name = $_REQUEST['Name'];
$tele = $_REQUEST['Tele'];
$city = $_REQUEST['City'];
// UNIQUE CONSTRAINT
$pg_no = $_REQUEST['pg_no']; //product
$date = $_REQUEST['Date']; //date
//checking if pg_no and Date are same
$check = mysqli_query($db_connect, "SELECT * FROM lstclient WHERE pg_no='{$pg_no}', Date='{$date}'");
{
echo "Already booked please select another date<br/>";
}
//if not same then insert data
else
{
$query = mysqli_query($db_connect, "INSERT INTO lstclient(pg_no,Name,Tele,City,Date) VALUES('$pg_no','$name','$tele','$city','$date')") or die(mysql_error());
}
mysqli_close($db_connect);
// messaging
if ($query) {
header("location:index.php?note=failed");
} else {
header("location:index.php?note=success");
}
?>

Answer 1

There are a few problems:
The file fails to parse because of the dangling else; it's not paired with an if-statement.
{
echo "Already booked please select another date<br/>";
}
//if not same then insert data
else
{
$query = mysqli_query($db_connect, "INSERT INTO lstclient(pg_no,Name,Tele,City,Date) VALUES('$pg_no','$name','$tele','$city','$date')") or die(mysql_error());
}
It looks like you're intending to use the result from your SELECT statement ($check), however...
The SELECT statement is invalid; WHERE clauses are separated with AND or OR, not commas.
When inserting the row into the database table, you're dying on mysql_error when you've been using the mysqli extension.
You're vulnerable to SQL injection attacks; if pg_no happened to be '; DELETE FROM users; --, as an example, your user table would be deleted. You're already using the mysqli extension, so use parameter binding and prepared statements. Reference