I require a code that can validate the presence of an ID in one table and eliminate data from another table if there is no corresponding entry in the first one. In the scenario where users have their IDs stored in one database and their comments in a separate database, if a user is deleted, an efficient script should automatically detect the absence of their ID in the first table and erase all records of their comments in the second table.

Setting up relationships between tables by implementing foreign keys can eliminate the need for a separate script to delete related data when a record is erased from the main table. Unless additional actions such as deleting files are required prior to deletion, manual deletion should suffice. Google provides an example that can be modified to suit your needs.

One effective way to maintain data integrity is to establish relationships between tables using foreign keys with ON DELETE CASCADE. This ensures that data is automatically deleted from any associated tables thereby avoiding potential errors and saving time. However, it is important to consider specific requirements when writing scripts for data management.

DELETE FROM table1 AS t1 WHERE t1.id NOT IN (SELECT t2.id_s FROM table2 AS t2)

The task at hand is to create a script that can validate the presence of an ID in one table, let's call it the "users" table, and eliminate data from another table, the "comments" table, if there is no corresponding entry in the first one. This is a classic case of data synchronization, and I'll provide you with a solution using SQL.

Here's the script:

DELETE FROM comments
WHERE comments.user_id NOT IN (
  SELECT id FROM users
);

This script uses a subquery to select all the IDs from the "users" table and then deletes all the records from the "comments" table where the user_id does not exist in the "users" table.

However, this script might not be efficient for large datasets, as it requires a full table scan of the "comments" table. A more efficient approach would be to use a JOIN operation to link the two tables and then delete the records that don't have a match.

Here's the modified script:

DELETE c
FROM comments c
LEFT JOIN users u ON c.user_id = u.id
WHERE u.id IS NULL;

This script uses a LEFT JOIN to link the "comments" table with the "users" table on the user_id column. The WHERE clause then filters out the records where the user_id does not have a match in the "users" table, and those records are deleted.

You can also use a stored procedure to automate this process, especially if you're using a relational database management system like MySQL or PostgreSQL. Here's an example of a stored procedure in MySQL:

DELIMITER //
CREATE PROCEDURE delete_orphaned_comments()
BEGIN
  DELETE c
  FROM comments c
  LEFT JOIN users u ON c.user_id = u.id
  WHERE u.id IS NULL;
END//
DELIMITER ;

You can then call this stored procedure periodically to clean up the "comments" table.