For instance, if you dump the table with mysqldump and then reload it, MySQL normally generates new sequence numbers when it encounters 0 values, resulting in a table with IDs which are different from the ones that were dumped. Note: starting at 0 is not recommended because it can lead to problems. Hence, all of the following statements are equivalent: INSERT INTO widgets (id, name, description) VALUES('another widget', NULL) INSERT INTO widgets (id, name, description) VALUES(0,'another widget', NULL) INSERT INTO widgets (id, name, description) VALUES(NULL,'another widget', NULL) Assigning NULL to the column will also generate the next sequence number, as long as the column was declared NOT NULL. You can also explicitly assign 0 to the column to generate the next sequence number unless the NO_AUTO_VALUE_ON_ZERO SQL mode is enabled. Selecting the contents of the widgets table will return three rows with id values of 1, 2, and 3 respectively: < SELECT * FROM widgets +-+-+-+ | id | name | description | +-+-+-+ | 1 | widget 1 | The first widget | | 2 | widget 2 | The second widget | | 3 | widget 3 | The third widget | +-+-+-+ Setting the AUTO_INCREMENT Column Valueīy default, the AUTO_INCREMENT column begins at 1. The AUTO_INCREMENT column will increase by one every time a new row in inserted, so you don’t have to include it in your INSERT statements: INSERT INTO widgets (name, description) VALUES ('widget 1', 'The first widget'), ('widget 2', 'The second widget'), ('widget 3', 'The third widget') Integer Types include INTEGER, INT, SMALLINT, TINYINT, MEDIUMINT, and BIGINT. For TINYINT UNSIGNED, the maximum grows to 255. For example, if you use TINYINT, the maximum permissible sequence number is a mere 127. You can always include the UNSIGNED attribute to allow a greater range. Should the column reach the upper limit of the data type, the next attempt to generate a sequence number will fail. You should use the smallest integer data type for the AUTO_INCREMENT column that is large enough to hold the maximum sequence value you anticipate accommodating. Typically, the AUTO_INCREMENT field is a type of INTEGER and is declared as the primary key column of the table: CREATE TABLE widgets ( id MEDIUMINT NOT NULL AUTO_INCREMENT, name CHAR(30) NOT NULL, description VARCHAR(255) NULL, PRIMARY KEY (id) )
To make a column that auto increments, simply assign the AUTO_INCREMENT attribute to it.
Mysql add column auto increment how to#
In this article, you’ll learn how to use AUTO_INCREMENT columns in MySQL, as well as explore a few unusual use cases. Although auto incrementing can be as simple as setting and forgetting it, there are times where you may want to manage the AUTO_INCREMENT column to set the start number or perhaps skip certain values. This feature is especially useful in the primary key field so that the key can be set automatically every time a new record is inserted. Auto-increment allows a unique number to be generated automatically whenever a new record is inserted into a table.
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