Setting a Primary Key 2 : Primary Key « Key « SQL / MySQL

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SQL / MySQL » Key » Primary Key 
Setting a Primary Key 2
  
/*
mysql> Drop TABLE Employee;
Query OK, 0 rows affected (0.00 sec)

mysql> CREATE TABLE Employee (
    ->    Name    VARCHAR(50) NOT NULL,
    ->    Phone VARCHAR(15) DEFAULT 'Unknown Phone' NOT NULL,
    ->    PRIMARY KEY (Name));
Query OK, 0 rows affected (0.06 sec)

mysql> Describe Employee;
+-------+-------------+------+-----+---------------+-------+
| Field | Type        | Null | Key | Default       | Extra |
+-------+-------------+------+-----+---------------+-------+
| Name  | varchar(50) |      | PRI |               |       |
| Phone | varchar(15) |      |     | Unknown Phone |       |
+-------+-------------+------+-----+---------------+-------+
2 rows in set (0.00 sec)

mysql> INSERT INTO Employee (Name, Phone) VALUES ('Joe Wang', '666 2323');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO Employee (Name) VALUES ('John Doe');
Query OK, 1 row affected (0.00 sec)

mysql> INSERT INTO Employee (Name, Phone) VALUES ('Joe Wang', NULL);
ERROR 1048 (23000): Column 'Phone' cannot be null
mysql> Select * from Employee;
+----------+---------------+
| Name     | Phone         |
+----------+---------------+
| Joe Wang  | 666 2323      |
| John Doe | Unknown Phone |
+----------+---------------+
2 rows in set (0.00 sec)


*/
Drop TABLE Employee;

CREATE TABLE Employee (
   Name    VARCHAR(50) NOT NULL, 
   Phone VARCHAR(15) DEFAULT 'Unknown Phone' NOT NULL,
   PRIMARY KEY (Name));

Describe Employee;

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

Select * from Employee;


           
         
    
  
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1.Setting a Primary Key 1
2.Setting a Primary Key 3
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16.Create a multiple-column primary key using UNIQUE, if the columns are declared NOT NULL
17.Using three column as the primary key
18.Drop primary key
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