To remove duplicate entries from a PostgreSQL JOIN table, you can use the DISTINCT keyword in the SELECT statement to eliminate identical rows, or you can use the GROUP BY clause to group the table by a specific column and remove the duplicates.
For example, suppose you have a JOIN table named "orders" that contains duplicate entries:
SELECT * FROM orders;
id | customer_id | product_id | quantity
----+-------------+------------+---------
1 | 101 | 201 | 2
2 | 102 | 202 | 3
3 | 101 | 201 | 1
4 | 103 | 203 | 4
To remove the duplicates, you can use the following query:
SELECT DISTINCT * FROM orders;
This query will return:
id | customer_id | product_id | quantity
----+-------------+------------+---------
1 | 101 | 201 | 2
2 | 102 | 202 | 3
3 | 101 | 201 | 1
4 | 103 | 203 | 4
Alternatively, you can use the GROUP BY clause to group the table by the customerid and productid columns and sum the quantity:
SELECT customer_id, product_id, SUM(quantity) FROM orders GROUP BY customer_id, product_id;
This query will return:
customer_id | product_id | sum
------------+------------+-----
101 | 201 | 3
102 | 202 | 3
103 | 203 | 4
In this case, the duplicates have been removed, and the total quantity for each customer and product is shown.
Please start posting anonymously - your entry will be published after you log in or create a new account. This space is reserved only for answers. If you would like to engage in a discussion, please instead post a comment under the question or an answer that you would like to discuss
Asked: 2023-06-02 02:54:21 +0000
Seen: 16 times
Last updated: Jun 02 '23
How can the SQL debug mode be activated in PostgreSQL version 15.2?
What is the procedure for using pg_restore on Windows with Docker?
What is the equivalent of SQL Server NVARCHAR in PostgreSQL?
What is the method to retrieve the JSON data from a column in SQL?
How to solve the issue of being unable to establish a connection with libpq on Mac M1?
Is it possible to launch multiple instances of PostgreSQL using Spring Boot Testcontainers?
Due to SyntaxError, why am I unable to create a TIMESTAMP WITH TIMEZONE column in postgres?