mysql-error-1093

I'm introducing database integrity using innodb constraints in the next version of my application. Everything goes well, but some of my tables have records with deleted references (dead records) and because of them I can't add constraints to the table. I am trying: ALTER TABLE `article` ADD FOREIGN KEY (`author_id`) REFERENCES `authors` (`id`) ON DELETE CASCADE; And I get: #1452 - Cannot add or update a child row: a foreign key constraint fails (`books`.<result 2 when explaining filename '#sql-442_dc'>, CONSTRAINT `#sql-442_dc_ibfk_1` FOREIGN KEY (`author_id`) REFERENCES `authors` (`id`) ON

I have a table 'employees' and I'm trying to set some attributes (e.g. salary) to the same value as some other value in the table. My understanding of this error is that it can be avoided with the following workaround, using a temporary table: UPDATE employees SET salary=(SELECT salary FROM (SELECT * FROM employees WHERE employee_id= '123') AS t1) WHERE employee_id='456'; However, I am still getting the same error code ("can't specify target table 'employees' for update in FROM clause") when I try this. Is there some other issue here? The issue is a functional change in mysql 5.7,scroll

UPDATE forms SET pos = (SELECT MIN(pos)-1 FROM forms) WHERE id=$id This doesn't work, error message: **You can't specify target table 'form' for update in FROM clause** I hope it's clear: I want to get the minimal element-1 from the same table and assign it to pos Consp is right that it's not supported. There's a workaround, however: UPDATE forms SET pos = (SELECT MIN(pos)-1 FROM (SELECT * FROM forms) AS x) WHERE id=$id A version that is probably faster: UPDATE forms SET pos = (SELECT pos-1 FROM (SELECT MIN(pos) AS pos FROM forms) AS x) where id=$id Your problem is stated plainly in the MySQL

I have got MySQL error "You can't specify target table 'tasks' for update in FROM clause" running the following query: DELETE FROM tasks WHERE tasks.id IN ( SELECT tasks.id FROM tasks JOIN deadlines ON deadlines.id = deadline_id WHERE DATE_ADD(tasks.created_at, INTERVAL deadlines.duration DAY) <= NOW() ) How can I manage this? Thanx! You can wrap it in a subquery like so. The issue is that MySQL can't update rows that it's also querying. This will make MySQL use a temporary table implicitly to store the ids you want to delete. DELETE FROM tasks WHERE tasks.id IN ( SELECT id FROM ( SELECT tasks

I am running many instances of a webcrawler in parallel. Each crawler selects a domain from a table, inserts that url and a start time into a log table, and then starts crawling the domain. Other parallel crawlers check the log table to see what domains are already being crawled before selecting their own domain to crawl. I need to prevent other crawlers from selecting a domain that has just been selected by another crawler but doesn't have a log entry yet. My best guess at how to do this is to lock the database from all other read/writes while one crawler selects a domain and inserts a row in