MySQL Create Table Exercises: Create a table countries, and make sure that no duplicate data in country_id will be allowed at run time

MySQL Create Tables: Exercise-9 with Solution

9. Write a SQL statement to create a table named countries including columns country_id,country_name and region_id and make sure that no duplicate data against column country_id will be allowed at the time of insertion.

Sample Solution:

CREATE TABLE IF NOT EXISTS countries ( 
COUNTRY_ID varchar(2) NOT NULL,
COUNTRY_NAME varchar(40) NOT NULL,
REGION_ID decimal(10,0) NOT NULL,
UNIQUE(COUNTRY_ID)
);

Let execute the above code in MySQL 5.6 command prompt

Here is the structure of the table:

mysql> DESC countries;
+--------------+---------------+------+-----+---------+-------+
| Field        | Type          | Null | Key | Default | Extra |
+--------------+---------------+------+-----+---------+-------+
| COUNTRY_ID   | varchar(2)    | YES  |     | NULL    |       |
| COUNTRY_NAME | varchar(40)   | YES  |     | NULL    |       |
| REGION_ID    | decimal(10,0) | YES  |     | NULL    |       |
+--------------+---------------+------+-----+---------+-------+
3 rows in set (0.01 sec)

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