check constraint in sql

1ALTER TABLE <table>
2ADD CONSTRAINT chk_val CHECK (col in ('yes','no','maybe'))

1CREATE TABLE Persons (
2    ID int NOT NULL,
3    LastName varchar(255) NOT NULL,
4    FirstName varchar(255),
5    Age int,
6    City varchar(255),
7    CONSTRAINT CHK_Person CHECK (Age>=18 AND City='Sandnes')
8);

1CREATE TABLE test(
2    _id BIGINT PRIMARY KEY NOT NULL,
3    decision NVARCHAR(5),
4    CHECK (decision in ('yes','no','maybe'))
5);

1#Add Check
2ALTER TABLE Persons
3ADD CONSTRAINT CHK_PersonAge CHECK (Age>=18 AND City='Sandnes');
4
5#Drop Check 
6ALTER TABLE Persons
7DROP CHECK CHK_PersonAge;

1#For one column
2CREATE TABLE Persons (
3    ID int NOT NULL,
4    LastName varchar(255) NOT NULL,
5    FirstName varchar(255),
6    Age int CHECK (Age>=18)
7);

1/*Adding Check constraint in sql server*/
2ALTER TABLE (Table_Name)
3ADD CONSTRAINT (Constraint_Name) CHECK (Boolean_Expression)