PostgreSQL Create Table: Create a table countries set a constraint NULL

5. Write a SQL statement to create a table countries, set a constraint NULL.

Sample Solution:

Code:

-- This SQL statement creates a new table named 'countries' if it does not already exist,
-- defining the structure and constraints for the table columns.

CREATE TABLE IF NOT EXISTS countries ( 
    COUNTRY_ID varchar(2) NOT NULL, -- Defines a column 'COUNTRY_ID' to store country IDs as strings with a maximum length of 2 characters. The column cannot contain NULL values.
    COUNTRY_NAME varchar(40) NOT NULL, -- Defines a column 'COUNTRY_NAME' to store country names as strings with a maximum length of 40 characters. The column cannot contain NULL values.
    REGION_ID decimal(10,0) NOT NULL -- Defines a column 'REGION_ID' to store region IDs as decimal numbers with a precision of 10 digits and no decimal places. The column cannot contain NULL values.
);

Explanation:

• The CREATE TABLE IF NOT EXISTS statement creates a new table only if it does not already exist in the database.
• The table is named 'countries'.
• Each column definition specifies the column name, data type, and optional constraints.
• varchar(2) indicates a variable-length character string with a maximum length of 2 characters for the 'COUNTRY_ID' column.
• varchar(40) indicates a variable-length character string with a maximum length of 40 characters for the 'COUNTRY_NAME' column.
• decimal(10,0) indicates a decimal number with a precision of 10 digits and no decimal places for the 'REGION_ID' column.
• The NOT NULL constraint ensures that each column must contain a value and cannot be left empty.

Output:

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

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

postgres=# \d countries;
           Table "public.countries"
    Column    |         Type          | Modifiers
--------------+-----------------------+-----------
 country_id   | character varying(2)  | not null
 country_name | character varying(40) | not null
 region_id    | numeric(10,0)         | not null

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

Previous: Write a SQL statement to create a duplicate copy of countries table, including structure and data by name dup_countries.
Next: Write a SQL statement to create a table named jobs, including job_id, job_title, min_salary, max_salary and check whether the max_salary amount exceeding the upper limit 25000.