MySQL INSERT IF NOT EXIST else DELETE row - mysql

Question

I have a table that links 2 other tables together.
I have a list of checkboxes, where when one is checked, it sends the value to the server via ajax.
What I want to do is if the values are not in the database, insert them (checked) or if they are there, delete them (unchecked)
Is there a way to do it without writing several queries? I know its not to hard with an insert/update, but what about delete?

Answer 1

You can allways delete and, if affected rows is 0, then insert. Easy, simple and it works.

Answer 2

INSERT IF NOT EXISTS ... is not available in MySQL (it is specific to T-SQL afaik). Use a transaction instead but keep in mind that not every MySQL engine supports transactions although no error is raised when using transactional statements.

Answer 3

This might help you out depending on your key structure http://bogdan.org.ua/2007/10/18/mysql-insert-if-not-exists-syntax.html
Otherwise you might be able to handle what you're doing with a subquery?

Answer 4

Not 100% what you are looking for, but it does the insert if not exists:
http://remy.supertext.ch/2010/11/mysqlupdate-and-insert-if-not-exists/
INSERT INTO wp_postmeta (post_id, meta_key) SELECT ?id, ‘page_title’
FROM DUAL WHERE NOT EXISTS (
SELECT meta_id FROM wp_postmeta WHERE post_id = ?id AND meta_key = ‘page_title’);
UPDATE wp_postmeta SET meta_value = ?page_title WHERE post_id = ?id AND meta_key = ‘page_title’;

Answer 5

There is no such thing as ON DUPLICATE DELETE or a correct use of IF ELSE with subqueries to do that in one query (which would be handy since this one query will either succeed or fail). Think you'd have to roll over several queries in achieving your goal, like I did. But keeping track on whether or not the subsequent queries keep succeeding.
Start out with a return value ('state' in this case) which is "Unknown" or "NoChange". If this returns to you ajax call, you know the checkbox needs to return to its previous state before clicking, and possible popup a message (which you can carry along with the json).
run your queries in a correct if/then code structure, and keep track of succeeding queries, and update the 'state' when a series succeeded accordingly.
This should do exactly what you need, keep it from having black holes.
(I use some wrappers for running queries, that return true/false/null/errorinformation - which allows you to check each query result)
I assume you have your ajax call in place already. The code example starts where your ajax call starts processing from the server side:
ob_end_clean();
$json = array("state" => "Unknown");
$module_id = (isset($_POST['module_id']) ? $_POST['module_id'] : null);
$group_id = (isset($_POST['group_id']) ? $_POST['group_id'] : null);
$action = (isset($_POST['action']) ? $_POST['action'] : null);
if (!empty($module_id) && !empty($group_id) && !empty($action)) {
$query = "
SELECT
1
FROM
config_module_actions_groups
WHERE
1
AND module_id = '{$module_id}'
AND group_id = '{$group_id}'
AND action = '{$action}'
";
if (getQueryAsArraySingleValues($query)) {
$query = "
DELETE FROM
config_module_actions_groups
WHERE
1
AND module_id = '{$module_id}'
AND group_id = '{$group_id}'
AND action = '{$action}'
";
if (executeQuery($query)) {
$json["state"] = "Off";
} else {
$json["message"] = "Not correctly deactivated";
}
} else {
$query = "
REPLACE INTO
config_module_actions_groups
SET
module_id = '{$module_id}',
group_id = '{$group_id}',
action = '{$action}'
";
if (executeQuery($query)) {
$json["state"] = "On";
} else {
$json["message"] = "Not correctly activated";
}
}
}
// output
echo json_encode($json);
exit;