PostgreSQL Create Table: Create a table to allow one of the columns of a table to contain only an auto-incremented value

11. 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.

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 SERIAL PRIMARY KEY, -- Defines an auto-incrementing integer column 'COUNTRY_ID' as the primary key for the table.
    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.
• SERIAL is a PostgreSQL data type that automatically generates a unique integer for each row inserted into the table. It is commonly used for primary key columns that need to be unique identifiers for each row.
• PRIMARY KEY constraint sets the 'COUNTRY_ID' column as the primary key for the table, ensuring uniqueness and providing a unique identifier for each row in the table.
• 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 'COUNTRY_NAME' and 'REGION_ID' columns cannot contain NULL values.

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Previous: Write a SQL statement to create a table named countries, including columns country_id, country_name and region_id and make sure that the country_id column will be a key field which will not contain any duplicate data at the time of insertion.
Next: Write a SQL statement to create a table countries, including country_id, country_name and region_id and make sure that the combination of columns country_id and region_id will be unique.