Check out example codes for "check sql". It will help you in understanding the concepts better.

Code Example 1

ALTER TABLE <table>
ADD CONSTRAINT chk_val CHECK (col in ('yes','no','maybe'))

Code Example 2

CREATE TABLE test(
    _id BIGINT PRIMARY KEY NOT NULL,
    decision NVARCHAR(5),
    CHECK (decision in ('yes','no','maybe'))
);

Code Example 3

CREATE TABLE Persons
(

    ID int NOT NULL,

   
LastName varchar(255) NOT NULL,

   
FirstName varchar(255),

   
Age int,

   
CHECK (Age>=18)

);

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