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!
The answer is
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
);
Turning off safe mode in Mysql workbench 6.3.4.0
Edit menu => Preferences => SQL Editor : Other section: click on "Safe updates" ... to uncheck option
I have a far more simple solution, it is working for me; it is also a workaround but might be usable and you dont have to change your settings. I assume you can use value that will never be there, then you use it on your WHERE clause
DELETE FROM MyTable WHERE MyField IS_NOT_EQUAL AnyValueNoItemOnMyFieldWillEverHave
I don't like that solution either too much, that's why I am here, but it works and it seems better than what it has been answered
You can trick MySQL into thinking you are actually specifying a primary key column. This allows you to "override" safe mode.
Assuming you have a table with an auto-incrementing numeric primary key, you could do the following:
DELETE FROM tbl WHERE id <> 0
Source: Stackoverflow.com