Day 42 – AUTO INCREMENT Field
In SQL, an AUTO INCREMENT field is a column that automatically generates a unique numeric value when a new row is inserted into a table. The AUTO INCREMENT field is often used as a primary key because it guarantees the uniqueness of each row in the table.
The syntax for defining an AUTO INCREMENT field varies depending on the database system being used. In MySQL, for example, the AUTO INCREMENT field is defined as follows:
CREATE TABLE table_name ( id INT AUTO_INCREMENT PRIMARY KEY, column1 datatype, column2 datatype, ..... );
In the above syntax,
id is the name of the AUTO INCREMENT field,
INT is the data type of the field,
AUTO_INCREMENT is the keyword that tells MySQL to generate a new value for the field automatically, and
PRIMARY KEY specifies that the field is the primary key for the table.
When a new row is inserted into the table, the AUTO INCREMENT field is automatically assigned the next available integer value. Each subsequent row inserted into the table will have a unique value for the AUTO INCREMENT field.
For example, let’s say we have a table named “employees” with columns “id”, “name”, and “salary”. We want to define an AUTO INCREMENT field for the “id” column. The CREATE TABLE statement for this table would be as follows:
CREATE TABLE employees ( id INT AUTO_INCREMENT PRIMARY KEY, name VARCHAR(50), salary DECIMAL(10,2) );
In the above example, we have defined an AUTO INCREMENT field for the “id” column of the “employees” table. When a new row is inserted into the table, the “id” field will be automatically assigned the next available integer value.
It is important to note that not all database systems support the AUTO INCREMENT field syntax. In Microsoft SQL Server, for example, the equivalent functionality is provided by the IDENTITY property, and in Oracle, it is provided by the SEQUENCE object.