PostgreSQL Create Table: Create a table to restrict the value of a column within some specified values

7. Write a SQL statement to create a table named countries, including country_id, country_name and region_id and make sure that no countries except Italy, India and China will be entered in the table.

Sample Solution:

Code:

CREATE TABLE IF NOT EXISTS countries ( 
COUNTRY_ID varchar(2),
COUNTRY_NAME varchar(40)
CHECK(COUNTRY_NAME IN('Italy','India','China')) ,
REGION_ID decimal(10,0)
);

Output:

postgres=# CREATE TABLE IF NOT EXISTS countries (
postgres(# COUNTRY_ID varchar(2),
postgres(# COUNTRY_NAME varchar(40)
postgres(# CHECK(COUNTRY_NAME IN('Italy','India','China')),
postgres(# REGION_ID decimal(10,0)
postgres(# );
CREATE TABLE

Here is the command to see the structure of the created table :

postgres=# \d countries;
           Table "public.countries"
    Column    |         Type          | Modifiers
--------------+-----------------------+-----------
 country_id   | character varying(2)  |
 country_name | character varying(40) |
 region_id    | numeric(10,0)         |
Check constraints:
    "countries_country_name_check" CHECK (country_name::text = 
	ANY (ARRAY['Italy'::character varying, 'India'::character varying, 
	'China'::character varying]::text[]))

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Next: Write a SQL statement to create a table named countries, including 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.