SQL query: Delete all records from the table except latest N?

You cannot delete the records that way, the main issue being that you cannot use a subquery to specify the value of a LIMIT clause.

This works (tested in MySQL 5.0.67):

DELETE FROM `table`
WHERE id NOT IN (
  SELECT id
  FROM (
    SELECT id
    FROM `table`
    ORDER BY id DESC
    LIMIT 42 -- keep this many records
  ) foo
);

The intermediate subquery is required. Without it we'd run into two errors:

1. SQL Error (1093): You can't specify target table 'table' for update in FROM clause - MySQL doesn't allow you to refer to the table you are deleting from within a direct subquery.
2. SQL Error (1235): This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery' - You can't use the LIMIT clause within a direct subquery of a NOT IN operator.

Fortunately, using an intermediate subquery allows us to bypass both of these limitations.

Nicole has pointed out this query can be optimised significantly for certain use cases (such as this one). I recommend reading that answer as well to see if it fits yours.

Unfortunately for all the answers given by other folks, you can't DELETE and SELECT from a given table in the same query.

DELETE FROM mytable WHERE id NOT IN (SELECT MAX(id) FROM mytable);

ERROR 1093 (HY000): You can't specify target table 'mytable' for update 
in FROM clause

Nor can MySQL support LIMIT in a subquery. These are limitations of MySQL.

DELETE FROM mytable WHERE id NOT IN 
  (SELECT id FROM mytable ORDER BY id DESC LIMIT 1);

ERROR 1235 (42000): This version of MySQL doesn't yet support 
'LIMIT & IN/ALL/ANY/SOME subquery'

The best answer I can come up with is to do this in two stages:

SELECT id FROM mytable ORDER BY id DESC LIMIT n; 

Collect the id's and make them into a comma-separated string:

DELETE FROM mytable WHERE id NOT IN ( ...comma-separated string... );

(Normally interpolating a comma-separate list into an SQL statement introduces some risk of SQL injection, but in this case the values are not coming from an untrusted source, they are known to be integer values from the database itself.)

note: Though this doesn't get the job done in a single query, sometimes a more simple, get-it-done solution is the most effective.

DELETE  i1.*
FROM    items i1
LEFT JOIN
        (
        SELECT  id
        FROM    items ii
        ORDER BY
                id DESC
        LIMIT 20
        ) i2
ON      i1.id = i2.id
WHERE   i2.id IS NULL

If your id is incremental then use something like

delete from table where id < (select max(id) from table)-N

DELETE FROM table WHERE ID NOT IN
(SELECT MAX(ID) ID FROM table)

DELETE FROM table WHERE id NOT IN (
    SELECT id FROM table ORDER BY id, desc LIMIT 0, 10
)

This should work as well:

DELETE FROM [table] 
INNER JOIN (
    SELECT [id] 
    FROM (
        SELECT [id] 
        FROM [table] 
        ORDER BY [id] DESC
        LIMIT N
    ) AS Temp
) AS Temp2 ON [table].[id] = [Temp2].[id]

Why not

DELETE FROM table ORDER BY id DESC LIMIT 1, 123456789

Just delete all but the first row (order is DESC!), using a very very large nummber as second LIMIT-argument. See here