MySQL Create Table Exercises: Create a table countries, and make sure that the combination of columns country_id and region_id will be unique

MySQL Create Tables: Exercise-13 with Solution

13. Write a SQL statement to create a table countries including columns country_id, country_name and region_id and make sure that the combination of columns country_id and region_id will be unique.

Sample Solution:

CREATE TABLE IF NOT EXISTS countries (
COUNTRY_ID varchar(2) NOT NULL UNIQUE DEFAULT '',
COUNTRY_NAME varchar(40) DEFAULT NULL,
REGION_ID decimal(10,0) NOT NULL,
PRIMARY KEY (COUNTRY_ID,REGION_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)    | NO   | PRI |         |       |
| COUNTRY_NAME | varchar(40)   | YES  |     | NULL    |       |
| REGION_ID    | decimal(10,0) | YES  |     | NULL    |       |
+--------------+---------------+------+-----+---------+-------+
3 rows in set (0.01 sec)

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Previous: Write a SQL statement to create a table countries including columns country_id, country_name and region_id and make sure that the column country_id will be unique and store an auto incremented value.
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