What are the keywords for self-increasing constraints in mysql?

MySQL's auto-increment constraint generates a unique incrementing ID value for each row through the AUTO_INCREMENT keyword. This constraint is suitable for integer data types. It can also be used in conjunction with the PRIMARY KEY (for primary key) and UNIQUE (for unique index) keywords, where the primary key cannot contain NULL values ​​and each value must be unique, while the unique index can contain NULL values ​​but other values ​​must be unique.

Auto-increment constraint keyword in MySQL

Auto-increment constraint in MySQL is used to set the Each row automatically generates a unique incrementing ID value. The following keywords are related to auto-increment constraints:

AUTO_INCREMENT

• Define auto-increment constraints for columns.
• This value is automatically incremented when a new row is inserted.
• This constraint can only be applied to integer data types (TINYINT, SMALLINT, MEDIUMINT, INT, BIGINT).

PRIMARY KEY

• You can specify an auto-increment column as the primary key.
• Primary key columns cannot contain NULL values, and each value must be unique in the table.

UNIQUE

• You can specify the auto-increment column as the only index.
• Unique index columns can contain NULL values, but other values ​​must be unique.

Example

CREATE TABLE customers (
  id INT NOT NULL AUTO_INCREMENT,
  name VARCHAR(255) NOT NULL,
  email VARCHAR(255) NOT NULL,
  PRIMARY KEY (id)
);

In this example, the id column has AUTO_INCREMENT and PRIMARY KEY constraint, so a uniquely incrementing ID value is automatically generated each time a new row is inserted.

The above is the detailed content of What are the keywords for self-increasing constraints in mysql?. For more information, please follow other related articles on the PHP Chinese website!