Summary: in this tutorial, you will learn how to use the MySQL generated columns to store data computed from an expression or other columns.
Introduction to MySQL generated column
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When you create a new table, you specify the table columns in the
CREATE TABLE statement. Then, you use the INSERT , UPDATE , and DELETE statements to modify directly the data in the table columns.
MySQL 5.7 introduced a new feature called the generated column. Columns are generated because the data in these columns are computed based on predefined expressions.
For example, you have the
contacts with the following structure:
To get the full name of a contact, you use the
CONCAT() function as follows:
This is not the most beautiful query yet.
By using the MySQL generated column, you can recreate the
contacts table as follows:
The
GENERATED ALWAYS as (expression) is the syntax for creating a generated column.
To test the
fullname column, you insert a row into the contacts table.
Now, you can query data from the
contacts table.
The values in the
fullname column are computed on the fly when you query data from the contacts table.
MySQL provides two types of generated columns: stored and virtual. The virtual columns are calculated on the fly each time data is read whereas the stored column are calculated and stored physically when the data is updated.
Based on this definition, the
fullname column that in the example above is a virtual column.
MySQL generated column’s syntax
The syntax for defining a generated column is as follows:
First, specify the column name and its data type.
Next, add the
GENERATED ALWAYS clause to indicate that the column is a generated column.
Then, indicate whether the type of the generated column by using the corresponding option:
VIRTUAL or STORED . By default, MySQL uses VIRTUAL if you don’t specify explicitly the type of the generated column.
After that, specify the expression within the braces after the
AS keyword. The expression can contain literals, built-in functions with no parameters, operators, or references to any column within the same table. If you use a function, it must be scalar and deterministic.
Finally, if the generated column is stored, you can define a unique constraint for it.
MySQL stored column example
Let’s look at the
products table in the sample database.
The data from
quantityInStock and buyPrice columns allow us to calculate the stock’s value per SKU using the following expression:
Auto_increment Not Primary Key Mysql
However, we can add a stored generated column named
stock_value to the products table using the following ALTER TABLE ...ADD COLUMN statement:
Typically, the
ALTER TABLE statement requires a full table rebuild, therefore, it is time-consuming if you change the big tables. However, this is not the case for the virtual column.
Now, we can query the stock value directly from the
products table.
In this tutorial, you have learned how to use the MySQL generated column to store data computed from an expression or other columns.
This MySQL tutorial explains how to create sequences using the AUTO_INCREMENT attribute in MySQL with syntax and examples.
Description
In MySQL, you can create a column that contains a sequence of numbers (1, 2, 3, and so on) by using the AUTO_INCREMENT attribute. The AUTO_INCREMENT attribute is used when you need to create a unique number to act as a primary key in a table.
Syntax
The syntax to create a sequence (or use the AUTO_INCREMENT attribute) in MySQL is:
Auto Generate Primary Key Sql
Note
![]() Example
Let's look at an example of how to use a sequence or the AUTO_INCREMENT attribute in MySQL.
For example:
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This MySQL AUTO_INCREMENT example creates a table called contacts which has 4 columns and one primary key:
Hibernate Auto Increment Primary Key Mysql
Set AUTO_INCREMENT starting value
Now that you've created a table using the AUTO_INCREMENT attribute, how can you change the starting value for the AUTO_INCREMENT field if you don't want to start at 1?
You can use the ALTER TABLE statement to change or set the next value assigned by the AUTO_INCREMENT.
Syntax
In MySQL, the syntax to change the starting value for an AUTO_INCREMENT column using the ALTER TABLE statement is:
Example
Let's look at an example of how to change the starting value for the AUTO_INCREMENT column in a table in MySQL.
For example:
Mysql Primary Key Syntax
This MySQL AUTO_INCREMENT example would change the next value in the AUTO_INCREMENT field (ie: next value in the sequence) to 50 for the contact_id field in the contacts table.
Drop Auto_increment Primary Key MysqlOther Related TutorialsAuto Generated Primary Key Mysql Database
Here are some other tutorials to help you learn more about sequences in MySQL:
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