MySQL delete in table problem
Because I have so many categories, I created a si开发者_Python百科ngle "categories" database table :
"id_category , parent_id , category_name , category_tag"
example :
----------------------------------------------------------
| id_category | parent_id | category_name | category_tag |
----------------------------------------------------------
| 1 | 0 | Cars | cars |
| 2 | 1 | Parts | parts |
| 3 | 2 | Accesories | accesories |
----------------------------------------------------------
the tree :
Cars
|_Parts
|_Accesories
My problem occurs when I want to delete all records in the tree. How do I delete all records in the tree branch from above example.
Is that possible in mySQL with PHP?
Look up InnodB
, that is type of database engine your site is probably using MyISAM
at the moment, also look up Cascade Deletes
.
InnobDb lets you assign relationships between indicies in your table, you can then assign an action as to what happens when a row is deleted or updated.
You want to set the ON DELETE
action to CASCADE
, this will cascade the delete operation to child rows and their child rows. So deleting a parent will automatically delete all children, grand children, etc.
http://dev.mysql.com/doc/refman/5.5/en/innodb-foreign-key-constraints.html
What you're looking for is a foreign key on parent_id that references id_category with constraint ON DELETE CASCADE. Then you can just delete the root element (category_id 0) and you should end up with an empty table.
A database table is not essentially a tree what you would normally do is
DELETE FROM categories WHERE id_category=3
or
DELETE FROM categories WHERE id_category=3 AND parent_id=2
If you don't have key with constraint, you can delete everything just by a TRUNCATE command on the table.
If you do have a key configured for cascade deletion, deleting the top item (parent_id=0) will delete all the depending and subdepending rows. In this case, deleting the first row would empty the table.
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