Question

I have a table in a mySQL database we’ll call ‘tbl’ where the fields are:

id, userID, favorite, emailID

The id is auto incremental. The userID stores an integer. The favorite is either yes or no. The emailID stores an integer.

I am programing in PHP and would like to have one query used to query the database that checks if the userID and emailID combination exists. If it does then update the favorite field with a yes or no value that comes from a form that is passed into the query dynamically. If it does not exist then insert the combination into the database.

Therefore if I had:

<?php
$userID = 34;
$emailID = 395;
$favorite = "yes"; // could be yes or no.

I don’t believe the query below is correct but gets the idea of what I am trying to do:

IF NOT EXISTS 
(SELECT userID, favorite, emailID 
FROM tbl 
WHERE ((userID = '$userID')and(emailID = '$emailID')) 
INSERT INTO tbl (userID, favorite, emailID) VALUES ('$userID', '$favorite', '$emailID')
ELSE UPDATE tbl
SET favorite = '$favorite'
WHERE ((userID = '$userID')and(emailID = '$emailID')) 

(please know that I know that entering values into a query like this is a security risk, this is only to help explain my question.)

What is the best way to write the query? Can it be written with one query?

Answer 1

I would drop the redundant id column and define the primary key as the combination of (userID, emailID), which means you have exactly one record for each different combination of the two fields, which seems to be what you want. Then you can use the REPLACE INTO command, which is equivalent to an INSERT but deletes any existing record if the primary key matches.