mysql delete under safe mode

 Googling around, the popular answer seems to be "just turn off safe mode":

SET SQL_SAFE_UPDATES = 0;
DELETE FROM instructor WHERE salary BETWEEN 13000 AND 15000;
SET SQL_SAFE_UPDATES = 1;

If I'm honest, I can't say I've ever made a habit of running in safe mode. Still, I'm not entirely comfortable with this answer since it just assumes you should go change your database config every time you run into a problem.

So, your second query is closer to the mark, but hits another problem: MySQL applies a few restrictions to subqueries, and one of them is that you can't modify a table while selecting from it in a subquery.

Quoting from the MySQL manual, Restrictions on Subqueries:

In general, you cannot modify a table and select from the same table in a subquery. For example, this limitation applies to statements of the following forms:

DELETE FROM t WHERE ... (SELECT ... FROM t ...);
UPDATE t ... WHERE col = (SELECT ... FROM t ...);
{INSERT|REPLACE} INTO t (SELECT ... FROM t ...);

Exception: The preceding prohibition does not apply if you are using a subquery for the modified table in the FROM clause. Example:

UPDATE t ... WHERE col = (SELECT * FROM (SELECT ... FROM t...) AS _t ...);

Here the result from the subquery in the FROM clause is stored as a temporary table, so the relevant rows in t have already been selected by the time the update to t takes place.

That last bit is your answer. Select target IDs in a temporary table, then delete by referencing the IDs in that table:

DELETE FROM instructor WHERE id IN (
  SELECT temp.id FROM (
    SELECT id FROM instructor WHERE salary BETWEEN 13000 AND 15000
  ) AS temp
);

SQLFiddle demo.