Using Auto-Increment value in MYSQL Before Insert Trigger?

Question

The users table:

CREATE TABLE `users` (
  `id` int(8) unsigned NOT NULL AUTO_INCREMENT,
  `email` varchar(45) DEFAULT NULL,
  `username` varchar(16) DEFAULT          


        

Answer 1

OP's comment:
How would I do it before, thou?

You can find current auto_increment value that is to be assigned to a new record.
And use the same in the before trigger as a parent user id for user_records table.
You have to query information_schema.tables table to find the value.

Example:

use `gknet`;

delimiter $$

drop trigger if exists before_create_user; $$

create definer=`root`@`localhost` trigger `before_create_user` 
       before insert on `users` 
for each row begin
  declare fk_parent_user_id int default 0;

  select auto_increment into fk_parent_user_id
    from information_schema.tables
   where table_name = 'users'
     and table_schema = database();

  insert into user_records ( action, userid, timestamp )
         values ( 'created', fk_parent_user_id, now() );
end;

$$

delimiter ;

Observations:
As per mysql documentation on last_insert_id(),

"if you insert multiple rows using a single INSERT statement, LAST_INSERT_ID() returns the value generated for the first inserted row only."

hence, depending on last_insert_id() and auto_increment field values in batch inserts seems not reliable.