Check if value exists before inserting into MySQL DB in a PHP script

Question

I've looked for similar questions with no success.

I have this piece of code:

form1.php

$query  = "INSERT INTO table1 ";
$query .= "(fname, lname, mail)";
$query .= " VALUES ";
$query .= "('".$_POST[fname]."', '".$_POST[lname]."', '".$_POST[mail]."')"; 

$result = mysql_query($query) or die ("Query Failed: " . mysql_error());

And I want that the script will check if the value inserted exists in the corresponding column, and throw an error if it does. any ideas?

Note: If you use stored procedures instead of inline queries you can maintain your code well and also it will give you advantages like compiled queries, syntax checking, prevent sql injection etc.... — dhinesh
– dhinesh, Commented Dec 8, 2010 at 6:53

Ignacio Vazquez-Abrams · Accepted Answer · 2010-12-08 06:03:40Z

11

Create a UNIQUE key on the fields you care about, and detect the integrity error after the fact.

answered Dec 8, 2010 at 6:03

Ignacio Vazquez-Abrams

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2 Comments

anon Over a year ago

This is really the only way, otherwise you end up with a race condition where failure goes unnoticed. If you check first and dump the record in if it's not already there, you're leaving open the possibility that someone could add the record in between your existence check and adding of the record.

Tom Granot Over a year ago

Thanks Ignacio Vazquez-Abrams and AgentConundrum!

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