update then replace dies - php

Question

If there is a row for user_id then I want to update, if not insert (but I was told to use replace). In the table there is id (which is primary key, auto inc) and user_id (index, session relates to). I have a form that when the data is changed it should be changed in the database for that particular user in session, otherwise it is just added for that particular user in session
if (empty($err)) {
$thesis_Name = mysql_real_escape_string($_POST['thesis_Name']);
$abstract = mysql_real_escape_string($_POST['abstract']);
$query="UPDATE thesis SET thesis_Name ='$thesis_Name',
abstract='$abstract' WHERE id='$_SESSION[user_id]'
IF ROW_COUNT()=0
REPLACE INTO thesis (thesis_Name,abstract)VALUES ('$thesis_Name', '$abstract')
";
mysql_query($query) or die();
// query is ok?
if (mysql_query($the_query, $link) ){
// redirect to user profile
header('Location: myaccount.php?id=' . $user_id);
}
With this the page just dies.
EDIT:
`thesis` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`user_id` int(11) NOT NULL,
`thesis_Name` varchar(200) NOT NULL,
`abstract` varchar(200) NOT NULL,
PRIMARY KEY (`id`),
KEY `user_id` (`user_id`)
)
Thanks so much

Answer 1

You don't need to do the UPDATE first - REPLACE handles all of this for you. From the MySQL manual:
REPLACE works exactly like INSERT, except that if an old row in the table has the same value as a new row for a PRIMARY KEY or a UNIQUE index, the old row is deleted before the new row is inserted. See Section 13.2.5, “INSERT Syntax”.
Therefore, so long as id is a unique key in your thesis table, the only SQL you need is:
REPLACE INTO thesis (id, thesis_Name, abstract)
VALUES ('$_SESSION[userid]', '$thesis_name', '$abstract');

Answer 2

There are a few things in your code that pose problem. First you don't have to do an insert and a replace in the same query : replace will insert if there is no row to replace (besides, I'm not even sure the sql syntax you're using is correct)...
Then you do a mysql_query($query) or die() which is probably where your code dies (maybe due to the fact that the sql syntax you used could be incorrect).
Right after that, you do a mysql_query again, which would reexecute the query a second time. Anyway, if your query didn't work, your code would have died on the previous line...
What you could do would be
$query = "REPLACE INTO blablabla";
if (!mysql_query($query))
echo "the query failed";
else header ("location:blabla");
but your query should mention for which user_id you want to update like this
REPLACE INTO thesis (id, thesis_Name, abstract)
VALUES ('{$_SESSION[userid]}', '$thesis_name', '$abstract');

Answer 3

INSERT
INTO thesis (id, abstract, thesis)
VALUES ('$_SESSION[user_id]', '$abstract', '$thesis_Name')
ON DUPLICATE KEY
UPDATE
abstract = VALUES(abstract),
thesis_Name = VALUES(thesis_Name)

Answer 4

You can do it with prepared statements.You can see an example sql ;
DROP PROCEDURE IF EXISTS `UPDATETHESIS`
|
CREATE PROCEDURE `UPDATETHESIS` (IN _id VARCHAR(50), IN _thesis_name VARCHAR(50), IN _abstract VARCHAR(50))
NOT DETERMINISTIC
CONTAINS SQL
SQL SECURITY INVOKER
IF EXISTS (SELECT * FROM thesis WHERE id = _id)
BEGIN
UPDATE thesis SET thesis_Name = _thesis_name,
abstract = _abstract WHERE id = _id
END
ELSE
BEGIN
INSERT INTO thesis (thesis_Name,abstract) VALUES (_thesis_name, _abstract)
END
You can call this like CALL UPDATETHESIS(userid, thesis_name, abstratc);