mysql delete under safe mode
mysql, sql
Solution
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.
Problem
I have a table instructor and I want to delete the records that have salary in a range An intuitive way is like this: ``` delete from instructor where salary between 13000 and 15000; ``` However, under safe mode, I cannot delete a record without providing a primary key(ID). So I write the following sql: ``` delete from instructor where ID in (select ID from instructor where salary between 13000 and 15000); ``` However, there is an error: ``` You can't specify target table 'instructor' for update in FROM clause ``` I am confused because when I write ``` select * from instructor where ID in (select ID from instructor where salary between 13000 and 15000); ``` it does not produce an error. My question is: - what does this error message really mean and why my code is wrong? - how to rewrite this code to make it work under safe mode? Thanks!