MySQL Update Query using a left join

Question

Table Schema

Table Name: file_manager_folder

Rows: id , parentId, name

My query

Answer 1

Kind of naive but how about this?

UPDATE file_manager_folder SET parentId = 54 
WHERE id IN( '1','2','3') 
AND parentId != 54 
AND name NOT IN (SELECT name FROM file_manager_folder WHERE id IN ('1', '2', '3'))

Answer 2

If you use an NOT IN instead of LEFT join that degrade your performance.

Run Explain before you query and the problem is obvious.

Answer 3

So you want to move folders only if a folder of the same name under the target parent folder does not exist:

UPDATE file_manager_folder f1
LEFT OUTER JOIN file_manager_folder f2 
    ON f1.name = f2.name AND f2.parentId = 54
SET f1.parentId = 54 
WHERE f2.name IS NULL AND f1.id IN (1,2,3);

The join condition searches for a folder with the same name under the target parent. The WHERE clause tests that no such folder exists (f2.name is null only if the outer join finds no match).

Answer 4

I think this should be solved using a unique constraint/index on the parentid and name columns. Otherwise, anyone with INSERT/UPDATE access to the table can circumvent your business rule.

CREATE UNIQUE INDEX blah_uk ON FILE_MANAGER_FOLDER(parentId, name) USING BTREE