Help with logic - php

Question

I have a number of objects. They can be sorted into groups. When a user "drags" an object into a group, I INSERT a record into my db
INSERT INTO t1
(group_id, item_id, project_id, user_id)
VALUES
($groupID, $itemID, $projectID, $userID)
There can be multiple objects in the same group and those objects can be moved from one group to another. When I move the objects into another group, I don't need to create another record, but rather only update group_id.
EDIT:
I think I need to do something like this afterall:
table structure
t1.id
t1.group_id
t1.item_id
t1.project_id
t1.user_id
if ("SELECT id, group_id FROM t1
WHERE item_id = $itemID
AND project_id = $projectID
AND user_id = $userID")) {
// if found
UPDATE t1
SET group_id = $groupID
WHERE id = $ID
} else {
INSERT INTO t1
(group_id, item_id, project_id, user_id)
VALUES ($groupID, $itemID, $projectID, $userID)

Answer 1

It sounds like u should place a if statement when moving from a group to another group to update only the object being move. Say for instance if I am selecting an object from its initial(beginning) space I would add the insert statement. If I am moving an object that has already been grouped to another group I would add an update statement. Finally if I am taking an item out of all groups completely I would issue a delete statement that will remove the object from the table.
pseudo code
if object = new
{
INSERT INTO t1 (group_id, item_id, project_id, user_id)
VALUES ($groupID, $itemID, $projectID, $userID)
}
if object = group
}
UPDATE t1
SET group_id = $newgroupID
WHERE item_id = $itemID;
}
if object = banned
}
delete from t1 where item_id = $itemID
}
This sequence of code should be placed on each container that you are dragging your objects to so that it can check for the proper requirements.

Answer 2

You can do it in one query using insert ... on duplicate key update.
See http://dev.mysql.com/doc/refman/5.5/en/insert-on-duplicate.html for details.
Assuming that item_id is a key, you can do
INSERT INTO t1
(group_id, item_id, project_id, user_id)
VALUES
($groupID, $itemID, $projectID, $userID)
ON DUPLICATE KEY UPDATE group_id = $groupID

Answer 3

I suggest you to add a surrogate primary key so you can you can identify uniquely every row. Then you can make an update like this:
UPDATE t1 SET group_id = $newgroupid WHERE id = $objectid;