SQL Challenges-1: Find all the writers who rated at least one of their own topic

SQL Challenges-1: Exercise-39 with Solution

From the following table write a SQL query to find all the writers who rated at least one of their own topic. Sorted the result in ascending order by writer id. Return writer ID.

Input:

Table: topics

Structure:

Data:

Sample Solution:

SQL Code(MySQL):

CREATE TABLE topics (topic_id int, writer_id int, rated_by int, date_of_rating date);
INSERT INTO topics VALUES (10001,504,507,'2020-07-17');
INSERT INTO topics VALUES (10003,502,503,'2020-09-22'); 
INSERT INTO topics VALUES (10001,503,507,'2020-02-07'); 
INSERT INTO topics VALUES (10002,501,507,'2020-05-13'); 
INSERT INTO topics VALUES (10002,502,502,'2020-04-10'); 
INSERT INTO topics VALUES (10002,504,502,'2020-11-16'); 
INSERT INTO topics VALUES (10003,501,502,'2020-10-05'); 
INSERT INTO topics VALUES (10001,507,507,'2020-12-23'); 
INSERT INTO topics VALUES (10004,503,501,'2020-08-28'); 
INSERT INTO topics VALUES (10003,505,504,'2020-12-21');  

SELECT DISTINCT writer_id AS 'Author rated on own topic'  
FROM topics
WHERE writer_id = rated_by
ORDER BY writer_id ;

Sample Output:

Author rated on own topic|
-------------------------|
                      502|
                      507|

SQL Code Editor:

Contribute your code and comments through Disqus.

Previous: Highest purchase for each customer.
Next: Writers who rated more than one topics on the same date.