PostgreSQL Create Table: Create a table to restrict the upper limit for a column

6. 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.

Sample Solution:

Code:

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

CREATE TABLE IF NOT EXISTS jobs ( 
    JOB_ID varchar(10) NOT NULL, -- Defines a column 'JOB_ID' to store job IDs as strings with a maximum length of 10 characters. The column cannot contain NULL values.
    JOB_TITLE varchar(35) NOT NULL, -- Defines a column 'JOB_TITLE' to store job titles as strings with a maximum length of 35 characters. The column cannot contain NULL values.
    MIN_SALARY decimal(6,0), -- Defines a column 'MIN_SALARY' to store minimum salary amounts as decimal numbers with a precision of 6 digits and no decimal places. This column can contain NULL values.
    MAX_SALARY decimal(6,0), -- Defines a column 'MAX_SALARY' to store maximum salary amounts as decimal numbers with a precision of 6 digits and no decimal places. This column can contain NULL values.
CHECK(MAX_SALARY<=25000) -- Defines a check constraint to ensure that the 'MAX_SALARY' value is less than or equal to 25000.
);

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 'jobs'.
• Each column definition specifies the column name, data type, and optional constraints.
• varchar(10) indicates a variable-length character string with a maximum length of 10 characters for the 'JOB_ID' column.
• varchar(35) indicates a variable-length character string with a maximum length of 35 characters for the 'JOB_TITLE' column.
.
• decimal(6,0) indicates a decimal number with a precision of 6 digits and no decimal places for both 'MIN_SALARY' and 'MAX_SALARY' columns.
• The NOT NULL constraint ensures that 'JOB_ID' and 'JOB_TITLE' columns cannot be left empty.
• The CHECK constraint ensures that the 'MAX_SALARY' value does not exceed 25000.

Output:

postgres=# CREATE TABLE IF NOT EXISTS jobs (
postgres(# JOB_ID varchar(10) NOT NULL ,
postgres(# JOB_TITLE varchar(35) NOT NULL,
postgres(# MIN_SALARY decimal(6,0),
postgres(# MAX_SALARY decimal(6,0)
postgres(# CHECK(MAX_SALARY<=25000)
postgres(# );
CREATE TABLE

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

postgres=# \d jobs;
             Table "public.jobs"
   Column   |         Type          | Modifiers
------------+-----------------------+-----------
 job_id     | character varying(10) | not null
 job_title  | character varying(35) | not null
 min_salary | numeric(6,0)          |
 max_salary | numeric(6,0)          |
Check constraints:
    "jobs_max_salary_check" CHECK (max_salary <= 25000::numeric)

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