Question

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What is the best way to insert into and update a single row table in MySQL?
handling duplicate records in mysql Insert statement

I have a php web form which inserts a record into my database when the ‘submit’ button is clicked. I would like however that if a record already exists in the database with the same primary key (itemID), the insert operation would be aborted and the user would be alerted.

My ‘insert’ code:

$editFormAction = $_SERVER['PHP_SELF'];
if (isset($_SERVER['QUERY_STRING'])) {
$editFormAction .= "?" . htmlentities($_SERVER['QUERY_STRING']);}

if ((isset($_POST["MM_insert"])) && ($_POST["MM_insert"] == "form1")) {
$insertSQL = sprintf("INSERT INTO inventory (itemID, name, itemcategory, qis, reorderlevel, unitcost, sellingprice,
supplier, specifications) VALUES (%s, %s, %s, %s, %s, %s, %s, %s, %s)",
 GetSQLValueString($_POST['itemID'], "text"),
 GetSQLValueString($_POST['name'], "text"),
 GetSQLValueString($_POST['itemcategory'], "text"),
 GetSQLValueString($_POST['qis'], "double"),
 GetSQLValueString($_POST['reorderlevel'], "int"),
 GetSQLValueString($_POST['unitcost'], "double"),
 GetSQLValueString($_POST['sellingprice'], "double"),
 GetSQLValueString($_POST['supplier'], "text"),
 GetSQLValueString($_POST['specifications'], "text"));

mysql_select_db($database_con1, $con1);
$Result1 = mysql_query($insertSQL, $con1) or die(mysql_error());

$insertGoTo = "insertsuccess.php";
if (isset($_SERVER['QUERY_STRING'])) {
$insertGoTo .= (strpos($insertGoTo, '?')) ? "&" : "?";
$insertGoTo .= $_SERVER['QUERY_STRING'];}

header(sprintf("Location: %s", $insertGoTo));}

Answer 1

If you define the ItemID column as a primary key in the table definition, the query will give you an error in case of duplicate keys. You can alert the user, in the error catch part.

Note: Mysql extensions are deprecated, use MYSQLi_* or PDO extensions instead.