I have a MySQL database which contains a table of users. The primary key of the table is 'userid', which is set to be an auto increment field.
What I'd like to do is when I insert a new user into the table is to use the same value that the auto increment is creating in the 'userid' field in a different field, 'default_assignment'.
e.g.
I'd like a statement like this:
INSERT INTO users ('username','default_assignment') VALUES ('barry', value_of_auto_increment_field())
so I create user 'Barry', the 'userid' is generated as being 16 (for example), but I also want the 'default_assignment' to have the same value of 16.
Is there any way to achieve this please?
Thanks!
Update:
Thanks for the replies. The default_assignment field isn't redundant. The default_assigment can reference any user within the users table. When creating a user I already have a form that allows a selection of another user as the default_assignment, however there are cases where it needs to be set to the same user, hence my question.
Update:
Ok, I've tried out the update triggers suggestion but still can't get this to work. Here's the trigger I've created:
CREATE TRIGGER default_assignment_self BEFORE INSERT ON `users`
FOR EACH ROW BEGIN
SET NEW.default_assignment = NEW.userid;
END;
When inserting a new user however the default_assignment is always set to 0.
If I manually set the userid then the default_assignment does get set to the userid.
Therefore the auto assignment generation process clearly happens after the trigger takes effect.
there's no need to create another table, and max() will have problems acording to the auto_increment value of the table, do this:
CREATE TRIGGER trigger_name BEFORE INSERT ON tbl FOR EACH ROW
BEGIN
DECLARE next_id INT; -- Specify the data type
SET information_schema_stats_expiry = 0; -- Without it, Won't work at MySQL8
SET next_id = (SELECT AUTO_INCREMENT FROM information_schema.TABLES WHERE TABLE_SCHEMA=DATABASE() AND TABLE_NAME='tbl');
SET NEW.field = next_id;
END
I declare the next_id variable because usually it will be used in some other way(*), but you could do straight new.field=(select ...)
CREATE TRIGGER trigger_name BEFORE INSERT ON tbl FOR EACH ROW
BEGIN
SET information_schema_stats_expiry = 0; -- Without it, Won't work at MySQL8
SET NEW.field=(SELECT AUTO_INCREMENT FROM information_schema.TABLES WHERE TABLE_SCHEMA=DATABASE() AND TABLE_NAME='tbl');
END
Also in cases of (SELECT string field) you can use CAST value;
CREATE TRIGGER trigger_name BEFORE INSERT ON tbl FOR EACH ROW
BEGIN
SET information_schema_stats_expiry = 0; -- Without it, Won't work at MySQL8
SET NEW.field=CAST((SELECT aStringField FROM information_schema.TABLES WHERE TABLE_SCHEMA=DATABASE() AND TABLE_NAME='tbl') AS UNSIGNED);
END
(*) To auto-name an image:
SET NEW.field = CONCAT('image_', next_id, '.gif');
(*) To create a hash:
SET NEW.field = CONCAT( MD5( next_id ) , MD5( FLOOR( RAND( ) *10000000 ) ) );