Question

I need a mechanism that inserts the data from a newly registered user to a database. I use PDO to do this, and this is my current code:

$dbc = new PDO('mysql:host=localhost;dbname=*****', *****, *****);

$insert_query = $dbc->prepare('INSERT INTO members(name, gender, email, pass)   
VALUES(:name, :gender, :email, :pass) WHERE email = :email LIMIT 1');

$insert_query->execute(array(':name' => $name, ':gender' =>    
$gender, ':email' => $email,  ':pass' => $pass));

However, nothing happens when a user submits the register form. I tried to echo $gender, $name, $email and $pass, and they all showed correct values. I am new to PDO, and I’m not sure what the problem could be at all. Is it a syntax error of some sort, or is it something else?

I don’t receive any error messages.

Answer 1

I don’t believe it is valid to include a LIMIT clause in an INSERT statement. LIMIT is not among the optional clauses in the MySQL INSERT syntax reference.

You also have a WHERE clause, which is also invalid in an INSERT statement.

I suspect you don’t have error reporting turned on, since this ought to have been a fatal error or thrown an exception if the statement failed to prepare() due to syntax errors. You would have gotten an error similar to

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ‘LIMIT 1’

$insert_query = $dbc->prepare('INSERT INTO members(name, gender, email, pass)   
VALUES(:name, :gender, :email, :pass) WHERE email = :email LIMIT 1');
//------------------------------------^^^^^^^^^^^^^^^^^^^^^^^^^^^

By definition, an INSERT statement inserts exactly as many rows as you have () groups^* for in your VALUES (), so there’s no need for a LIMIT anyway. You could use a LIMIT in an INSERT INTO...SELECT... statement, but in that case, the LIMIT is a clause of the SELECT component rather than the INSERT.

^* Ignoring potential key violations or other insert problems, obviously

The fact that you have conflated multiple components (WHERE,LIMIT) from UPDATE statements makes me wonder if you actually intended this to be an UPDATE rather than an INSERT statement to begin with. INSERT is only for new rows. UPDATE is for changing existing rows, and both WHERE and LIMIT are valid in UPDATE.

That would look like:

$upd_query = $dbc->prepare('UPDATE members SET name = :name, gender = :gender, email = :email, pass = :pass) WHERE email = :email LIMIT 1');