SQL Delete Mimicking Left Join

Brian Manning — Tue, 01 Dec 2009 08:35:32 +0000

It may seem a little silly, but sometimes I wish I could do something like a JOIN when I’m using DELETE. I came up with a workaround that does the job nicely (but maybe not efficiently, but hey, I don’t need to do this too often anyway).

DELETE FROM first_table WHERE ft_id IN (
  SELECT ft_id FROM first_table f
  LEFT JOIN second_table s ON s.ft_id = f.ft_id
  WHERE s.ft_id IS NOT NULL
  AND s.ft_id NOT IN (
    SELECT third_table.id
    FROM third_table
    WHERE id > 100))

I like it because just by using a IN using a primary key you can select any particular entry you wanted to delete. And it’s a whole lot safer because you can test by just using the SELECT by itself.

Using an Insert-Select Statement

Brian Manning — Sat, 31 Oct 2009 03:04:32 +0000

So, one other thing I want to use this blog for is recording stuff that I forget all the time. I feel like it especially happens with SQL. Why? Not quite sure. I’m a big fan of ActiveRecord, so that gets me away from SQL, so that could be it.

Anyway, I want to record it here because I always forget it: how to INSERT from one table using a SELECT from another table.

INSERT INTO sometable (acolumn, anothercolumn)
SELECT someothercolumn, onemorecolumn
FROM adifferenttable

Real simple, but I always end up second-guessing myself (stupidly, I know). Anyway, there it is so I won’t forget it… Hopefully…

Bri Manning's Blog » SQL

SQL Delete Mimicking Left Join

Using an Insert-Select Statement