Can MySQL Use Functions to Set Default Column Values?

Assigning Default Values with Functions in MySQL

In MySQL, default values for table columns are typically set as static values, such as constants or expressions. However, some users may encounter instances where they wish to assign default values using functions. This question explores whether such functionality is supported in MySQL.

Question:

Can MySQL assign default column values using functions? For example, can the following statement be executed successfully?

create table app_users
(
    app_user_id smallint(6) not null auto_increment primary key,
    api_key     char(36) not null default uuid()
);

Answer:

No, MySQL does not allow assigning default column values using functions. Attempts to do so will result in an error.

Solution:

While MySQL itself does not support function-based default values, a workaround can be achieved using triggers. Here's an example trigger that assigns a default UUID value to the api_key column before inserting a new row into the app_users table:

CREATE TRIGGER before_insert_app_users
  BEFORE INSERT ON app_users 
  FOR EACH ROW
  SET new.api_key = uuid();

This trigger will automatically generate and assign a new UUID to the api_key column for each new row inserted into the app_users table.

The above is the detailed content of Can MySQL Use Functions to Set Default Column Values?. For more information, please follow other related articles on the PHP Chinese website!