返回不存在的ID

Question

I have a list of IDs and I write a MYSQL query to get information about these IDs.

What I need is a way to figure out which IDs are no longer in the database to delete them from the list of IDs.

Is there an easy solution to do that which I just can't think of right now?

Answer 1

Create an additional (temporary) table, populate it with a list of IDs, and execute the query to find non existing id. For example -

CREATE TEMPORARY TABLE temp(id INT);
INSERT INTO temp VALUES (1), (2), (8), (10);

-- View non existing ID:
SELECT t.id FROM temp t
  LEFT JOIN your_table a 
    ON a.id = t.id
  WHERE a.id IS NULL;

DROP TEMPORARY TABLE IF EXISTS temp;

Then read this dataset in php application and update the list of IDs.

Answer 2

This is written not knowing your table structure, and thus making one up off the top of my head, but...

If you have two tables, ID and INFO, like:

ID (IDCOL int, DATEENTERED datetime)
INFO (INFOID int, ID_ID int, ID_NAME varchar(50))

Then you could query

SELECT * FROM ID WHERE IDCOL NOT IN (SELECT ID_ID FROM INFO)

And that should return all entries in ID where there is not corresponding entry in INFO.

After that it's a case of writing appropriate delete statements.

The whole thing could be done in one step with

DELETE FROM ID WHERE IDCOL NOT IN (SELECT ID_ID FROM INFO)

But I generally prefer to do my deletes in defined transactions where you can examine to make sure you haven't screwed it up before you commit the changes to the DB.