How to count newly inserted row like facebook news feed

A great question!

Counting newly inserted rows like Facebook's news feed is a common problem in database systems. Here are a few approaches to achieve this:

Method 1: Using a trigger

Create a trigger that fires after each insert operation on the table. The trigger can update a separate table or a column in the same table to keep track of the newly inserted rows.

For example, let's say you have a table posts and you want to count the newly inserted rows. You can create a trigger like this:

CREATE TRIGGER trg_post_insert
AFTER INSERT ON posts
FOR EACH ROW
BEGIN
    UPDATE post_counts SET count = count + 1;
END;

In this example, the trigger updates a separate table post_counts to increment the count column by 1 after each insert operation on the posts table.

Method 2: Using a timestamp and a query

Another approach is to use a timestamp column in the table and a query to count the newly inserted rows based on the timestamp.

For example, let's say you have a table posts with a timestamp column created_at. You can use a query like this:

SELECT COUNT(*) FROM posts WHERE created_at > (SELECT MAX(created_at) FROM posts) - INTERVAL 1 MINUTE;

This query counts the number of rows inserted in the last minute by filtering the rows with a timestamp greater than the maximum timestamp minus 1 minute.

Method 3: Using a materialized view

Some databases, like Oracle, support materialized views, which can be used to count newly inserted rows.

For example, you can create a materialized view like this:

CREATE MATERIALIZED VIEW post_counts AS
SELECT COUNT(*) FROM posts;

The materialized view will be updated automatically whenever the underlying table posts is modified.

Method 4: Using a caching layer

Another approach is to use a caching layer, like Redis or Memcached, to store the count of newly inserted rows. When a new row is inserted, the caching layer can be updated to reflect the new count.

For example, you can use a Redis command like this:

INSERT INTO posts...;
INCRBY post_count 1;

This approach requires a separate caching layer, but it can provide a high-performance solution for counting newly inserted rows.

These are just a few examples of how you can count newly inserted rows like Facebook's news feed. The choice of method depends on your specific use case, database system, and performance requirements.