how to remove data duplicacy in customer table - php

Question

i have a table customer_stock_entries.. i want to insert the item if the item and supplier is not available and i want to update the item if item and supplier is available
Example in my table i have stock_supplier_name and quantity. What i want to do is that if the stock supplier name entry is new then insert it into the table and if the entry is already there then delete the previous value in column 'quantity' and insert the new value.
i am stuck with this. Please help me out
I have tried something like this.
for ($i = 0; $i < count($stock_name); $i++) {
$count = $db->countOf("customer_stock", "name='$stock_name[$i]'");
if ($count == 0) {
$db->query("insert into customer_stock(name,quantity) values('$stock_name[$i]',$quty[$i])");
echo "<br><font color=green size=+1 >New Stock Entry Inserted !</font>";
$db->query("insert into stock_details(stock_id,stock_name,stock_quatity,supplier_id,company_price,selling_price) values('$autoid','$stock_name[$i]',0,'$supplier','$cost[$i]','$sell[$i]')");
$db->query("INSERT INTO customer_stock_entries(stock_id,stock_name, stock_supplier_name, quantity, company_price, selling_price, opening_stock, closing_stock, date, username, type, total, payment, balance, mode, description, due, subtotal,count1,billnumber) VALUES ( '$autoid1','$stock_name[$i]','$supplier','$quty[$i]','$cost[$i]','$sell[$i]',0,'$quty[$i]','$date','$username','entry','$total[$i]','$payment','$balance','$mode','$description','$due','$subtotal',$i+1,'$bill_no')");
} else if ($count == 1) {
$amount = $db->queryUniqueValue("SELECT quantity FROM customer_stock WHERE name='$stock_name[$i]'");
$amount1 = $amount + $quty[$i];
$db->execute("UPDATE customer_stock SET quantity='$amount' WHERE name='$stock_name[$i]'");
$db->query("INSERT INTO customer_stock_entries(stock_id,stock_name,stock_supplier_name,quantity,company_price,selling_price,opening_stock,closing_stock,date,username,type,total,payment,balance,mode,description,due,subtotal,count1,billnumber) VALUES ('$autoid1','$stock_name[$i]','$supplier','$quty[$i]','$cost[$i]','$sell[$i]','$amount','$amount1','$date','$username','entry','$total[$i]','$payment','$balance','$mode','$description','$due','$subtotal',$i+1,'$bill_no')");
Thanks

Answer 1

Typical solution to this problem involve following typical steps:
Check if the record for the stock supplier exists by using a select query and if it exists, update the quantity attribute.
If the the record doesn't exist, then insert the record in the table.
Sample Code as requested:
IF EXISTS(SELECT * FROM Users WHERE UserId = #UserId)
BEGIN
UPDATE TC_Users SET Salary = 25000 WHERE UserId = #UserId
END
ELSE
BEGIN
INSERT INTO TC_Users(UserId, Salary) VALUES(#UserId, 25000)
END
Hope this helps you.

Answer 2

Hare are some information's regarding your problem:
Primary Keys (To Avoid Duplication Of Data) :
Always use primary keys in your Database Table Structure i.e consider one column as primary key in order for it to be unique so that duplicate value won't be able to be inserted in your records.
Example : For instance I have a table with following columns as id,username,password,name .Now in order for to avoid duplication of data i.e that I don't want people to register with same username which means that username column value should be unique so instead I mark my username column as Primary Key.So now the new upcoming members won't be able to register with the same username which is already available in database i.e someone already registered using that username.Instead they will be needed to register with unique username.
Solution :
While here is code for to update your quantity value if supplier is already present in the database and if not so then insert the new record..!
$supplier_name = $_POST['supplier];
$query = mysqli_query($mysqli,"SELECT * FROM table");
$results = mysqli_fetch_array($query);
for ($i=0;$i<=count($results);$i++) {
//IF supplier is available in database
if ($results[$i]['supplier'] == $supplier_name) {
$query = mysqli_query($mysqli,"UPDATE table SET quantity=$quanity_new_value WHERE supplier=$supplier_name");
} else {
// If supplier is not available in database so it will insert new record
$query = mysqli_query($mysqli,"INSERT INTO table (supplier, quanity, email) VALUES ($supplier_name, $quantity, $email)");
}
}