In this example, the full_name column will automatically store the concatenation of the first_name and last_name columns. Let’s now see the generated column syntax in action in a CREATE TABLE query:įull_name varchar(120) GENERATED ALWAYS AS (CONCAT(first_name, ' ', last_name)) By default, if not explicitly specified in the query, MySQL marks a generated column as VIRTUAL. You will learn the difference between the two types in the chapter below. Then, you can indicate whether the type of the generated column is VIRTUAL or STORED. You can also precede AS with the GENERATED ALWAYS keywords to make the generated nature of the column more explicit, but this is optional. For example, you cannot use the CURDATE() function that returns the current date in a generated column expression definition because it is a mutable function. Also, notice that the generation expression can only involve immutable functions. The generation_expression defines the expression that MySQL will use to compute the column values, and it cannot reference another generated column or anything other than the columns of the current table. The AS (generated_column_expression) clause specifies that the column you are adding or updating to a table is a generated column. Generate_column_name column_type AS (generation_expression) Notice that generated columns are different from SQL triggers, and you can define them only when using CREATE TABLE or ALTER TABLE statements with the syntax below: In other words, you can think of a generated column as a sort of view but limited to columns. So, a generated column works within the domain of a table, and its definition cannot involve JOIN statements. This is because an expression defines how to generate the value of a generated column based on the other values that are read from the other columns of the same row. What is a MySQL Generated Column?Ī generated column is similar to a normal column, but you cannot change its value manually. Let’s now learn everything you need to know to master generated columns in MySQL. Also, generated columns can help you make your query easier and more efficient. This useful feature has been part of MySQL since version 5.7, and it represents an alternative approach to triggers when it comes to generating data. Generated columns allow you to store automatically generated data in a table without using the INSERT and UPDATE clauses. MySQL generated columns pose as a powerful, easy-to-use, and advanced tool for anyone who wants to add automatically generated data to their tables - in this blog, we will learn everything you need to know to master them.
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