mysqlan expression of a check

In MySQL, you can use the `CHECK` constraint to define a condition that must be satisfied before a row can be inserted or updated. The syntax for creating a `CHECK` constraint is as follows:

CREATE TABLE table_name (
  column1 datatype,
  column2 datatype,
  ...
  CONSTRAINT constraint_name CHECK (condition)
);

Here, `constraint_name` is the name of the constraint and `condition` is the condition that must be satisfied. For example, if you have a table for storing information about employees and you want to make sure that the salary is greater than or equal to 0, you can use the following `CHECK` constraint:

CREATE TABLE employees (
  id INT PRIMARY KEY,
  name VARCHAR(50),
  salary DECIMAL(10, 2),
  CONSTRAINT salary_check CHECK (salary >= 0)
);

This will ensure that any row inserted or updated in the `employees` table will have a salary that is greater than or equal to 0.