add check constraint in sql code example

Example 1: sql constraint check value in list

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

Example 2: check constraint in sql

CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int,
    City varchar(255),
    CONSTRAINT CHK_Person CHECK (Age>=18 AND City='Sandnes')
);

Example 3: sql constraint check value in list

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

Example 4: check constraint in sql

#Add Check
ALTER TABLE Persons
ADD CONSTRAINT CHK_PersonAge CHECK (Age>=18 AND City='Sandnes');

#Drop Check 
ALTER TABLE Persons
DROP CHECK CHK_PersonAge;

Example 5: check constraint in sql

#For one column
CREATE TABLE Persons (
    ID int NOT NULL,
    LastName varchar(255) NOT NULL,
    FirstName varchar(255),
    Age int CHECK (Age>=18)
);

Example 6: sql check

Adds a constraint that limits the value which can be added to a column.
Example 1 (MySQL): Makes sure any users added to the users table are 18
or over.
CREATE TABLE users (
first_name varchar(255),
age int,
CHECK (age>=18)
);
Example 2 (MySQL): Adds a check after the table has already been
created.
ALTER TABLE users
ADD CHECK (age>=18);