What is the purpose of auto increment?
Auto-increment allows a unique number to be generated automatically when a new record is inserted into a table. Often this is the primary key field that we would like to be created automatically every time a new record is inserted.
Is PRIMARY KEY auto increment by default?
AUTO_INCREMENT columns start from 1 by default. The automatically generated value can never be lower than 0. Each table can have only one AUTO_INCREMENT column. In some storage engines (including the default InnoDB), if the key consists of multiple columns, the AUTO_INCREMENT column must be the first column.
When do you use auto increment in MySQL?
In this case (when the AUTO_INCREMENT column is part of a multiple-column index), AUTO_INCREMENT values are reused if you delete the row with the biggest AUTO_INCREMENT value in any group. This happens even for MyISAM tables, for which AUTO_INCREMENT values normally are not reused.
Where to set auto increment value in InnoDB?
To start with an AUTO_INCREMENT value other than 1, set that value with CREATE TABLE or ALTER TABLE , like this: For information about AUTO_INCREMENT usage specific to InnoDB, see AUTO_INCREMENT Handling in InnoDB . For MyISAM tables, you can specify AUTO_INCREMENT on a secondary column in a multiple-column index.
What happens when auto increment value is skipped?
Mind that if you have transactions where you INSERT a row and rollback the transaction, that auto_increment value will be gone/skipped. In all lock modes (0, 1, and 2), if a transaction that generated auto-increment values rolls back, those auto-increment values are “lost”.
Why is my auto increment not working in Laravel?
Once a value is generated for an auto-increment column, it cannot be rolled back, whether or not the “INSERT-like” statement is completed, and whether or not the containing transaction is rolled back. Such lost values are not reused. Thus, there may be gaps in the values stored in an AUTO_INCREMENT column of a table.