PostgreSQL Insert Record: Insert one row into a table to ensure that no duplicate values will be entered in the key column

7. Write a SQL statement to insert one row in the jobs table to ensure that no duplicate values will be entered into the job_id column.

Sample Solution:

Code:

Here is the code to create a sample table jobs:

-- This SQL statement creates a new table named 'jobs' with specified columns and constraints.

CREATE TABLE jobs ( 
    JOB_ID integer NOT NULL UNIQUE,      -- Defines the JOB_ID column as an integer type, which cannot be NULL and must be unique
    JOB_TITLE varchar(35) NOT NULL,     -- Defines the JOB_TITLE column as a varchar type with a maximum length of 35 characters, which cannot be NULL
    MIN_SALARY decimal(6,0)              -- Defines the MIN_SALARY column as a decimal type with a precision of 6 digits and 0 decimal places
);

Explanation:

• The CREATE TABLE statement is used to create a new table in the database.
• jobs is the name of the new table being created.
• (JOB_ID integer NOT NULL UNIQUE, JOB_TITLE varchar(35) NOT NULL, MIN_SALARY decimal(6,0)) specifies the columns of the table along with their data types and constraints.
• JOB_ID is defined as an integer type column that cannot contain NULL values (NOT NULL) and must have unique values (UNIQUE constraint).
• JOB_TITLE is defined as a varchar type column with a maximum length of 35 characters and cannot contain NULL values.
• MIN_SALARY is defined as a decimal type column with a precision of 6 digits and 0 decimal places.

Now insert a row into the table jobs :

INSERT INTO jobs VALUES(1001,'OFFICER',8000);

Here is the command to see the list of inserting rows :

postgres=# SELECT * FROM jobs;
 job_id | job_title | min_salary
--------+-----------+------------
   1001 | OFFICER   |       8000
(1 row)

Now, try to insert the duplicate value in the key column and see what happen :

postgres=# INSERT INTO jobs VALUES(1001,'OFFICER',8000);
ERROR:  duplicate key value violates unique constraint "jobs_job_id_key"
DETAIL:  Key (job_id)=(1001) already exists.

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