Setting CHECK Constraints : Constraint « Table Index « SQL / MySQL

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2. Table Index
3. Constraint

Setting CHECK Constraints

 
/*
mysql> Drop TABLE Employee;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE Employee (
    ->    Name    VARCHAR(50) PRIMARY KEY NOT NULL,
    ->    PhoneNo VARCHAR(15) DEFAULT 'Unknown Phone',
    ->    Age     INT CHECK (Age BETWEEN 20 and 30));
Query OK, 0 rows affected (0.07 sec)

mysql> Describe Employee;
+---------+-------------+------+-----+---------------+-------+
| Field   | Type        | Null | Key | Default       | Extra |
+---------+-------------+------+-----+---------------+-------+
| Name    | varchar(50) |      | PRI |               |       |
| PhoneNo | varchar(15) | YES  |     | Unknown Phone |       |
| Age     | int(11)     | YES  |     | NULL          |       |
+---------+-------------+------+-----+---------------+-------+
3 rows in set (0.00 sec)

mysql> INSERT INTO Employee (Name, Phone, Age) VALUES ('Joe Wang', '666 2323', 26
);
ERROR 1054 (42S22): Unknown column 'Phone' in 'field list'
mysql> INSERT INTO Employee (Name, Age) VALUES ('John Doe', 31);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO Employee (Name, Phone) VALUES ('Joe Wang', NULL);
ERROR 1054 (42S22): Unknown column 'Phone' in 'field list'
mysql> Select * from Employee;
+----------+---------------+------+
| Name     | PhoneNo       | Age  |
+----------+---------------+------+
| John Doe | Unknown Phone |   31 |
+----------+---------------+------+
1 row in set (0.00 sec)


*/
Drop TABLE Employee;       
       
CREATE TABLE Employee (
   Name    VARCHAR(50) PRIMARY KEY NOT NULL, 
   PhoneNo VARCHAR(15) DEFAULT 'Unknown Phone',
   Age     INT CHECK (Age BETWEEN 20 and 30));

Describe Employee;

INSERT INTO Employee (Name, Phone, Age) VALUES ('Joe Wang', '666 2323', 26);
INSERT INTO Employee (Name, Age) VALUES ('John Doe', 31);
INSERT INTO Employee (Name, Phone) VALUES ('Joe Wang', NULL);

Select * from Employee;

           
         
  

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