how to get the auto-increment primary key of a table

Question

I have a small MySQL database of sellers where there is a table, in which each seller has an auto-increment primary key (and there is not any other unique key attribute). Now I want to retrieve each seller data from the php script

// Nothing wrong with this code
    $stmt = $this->conn->prepare("SELECT * FROM seller WHERE id= ? LIMIT 1");
    $stmt->bind_param("i", $ud);
    $stmt->execute();
    $result = $stmt->get_result();

But.. to retrieve data with this query, I need to have the primary key ( ie autoincrement id of the seller ). How would I know what is the primary key of the record inserted?

Answer 1

You would get the ID from your own data. For example, let's say you have a page where you list your Widget records. The database query on that page might be something like:

SELECT id,name FROM widgets

Then you'd display the output in a loop. Within this output, you might have a link such as:

echo '<a href="edit.php?id=' . $row['id'] . '">Edit</a>";

Which would output something like:

<a href="edit.php?id=123">Edit</a>

When clicking that link, your browser would then go to edit.php with the query string data id=123 . So on that page you could get that query string value:

$_GET['id']

That value would be the ID of the specific record you want to display. Use that as the parameter in your query:

SELECT * FROM widgets WHERE id=?

Or, in your specific code, that's the value you'd pass to your function:

getUserData($_GET['id'])

However you design it, the point is that you get the IDs from your data. You don't need to intuitively know what they are.

Answer 2

1. As you are trying to retrieve seller data from MySQL server based on an auto_increment id attribute. I assume that initially you are unaware of any details inside the table beforehand.

   This can be handled using PHP by, initially retrieving all id's in the table, along with a partially identifying attribute like seller name and thereafter, fetching all details of the required seller using the selected id.

    if(!$con) die(); function fetchId(){ $result = mysqli_query($con,"SELECT id, name FROM seller"); if($result && mysqli_num_rows($result)>0){ while($row = mysqli_fetch_assoc($result)){ echo "ID: ".$row["id"]." NAME: ".$row["name"]; retrieveData($row["id"]); } } } function retrieveData($id){ $result = mysqli_query($con,"SELECT * FROM seller WHERE id=".mysqli_real_escape_string($con,$id)); if($result && mysqli_num_rows($result)==1){ $row = mysqli_fetch_assoc($result) print_r($row); } } mysqli_close($con); 

2. Using auto_increment for an attribute like primary key is not a wrong approach when needing to retrieve data, but some partial rows containing the key are to be pre-fetched before the desired row can be individually accessed using it.

Answer 3

insert_id attribute of the prepared statement saved me. Now just after my insert statement I can get the last inserted primary key of the table-

$stmt->execute();
$sid = $stmt->insert_id;

This is equivalent to the LAST_INSERT_ID() function in mysql. Make sure you use this in the same session, just after insertion of the table row. Otherwise, it returns a null set.