Implicit joins, also known as implicit inner joins, are a shorthand way of performing an inner join in SQL. Instead of explicitly using the INNER JOIN keyword, you specify the tables you want to join in the FROM clause and specify the join condition in the WHERE clause. Implicit joins are generally less recommended than explicit joins (using INNER JOIN) because they can make your SQL code less readable and may not work in all database systems.

Here's an example of an implicit join:

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SELECT orders.order_id, customers.customer_name
FROM orders, customers
WHERE orders.customer_id = customers.customer_id;

In the above query:

• We specify both the orders and customers tables in the FROM clause.
• We define the join condition in the WHERE clause using orders.customer_id = customers.customer_id.

While this approach is valid SQL and will work in most relational database systems, it has some disadvantages:

1. Readability: Implicit joins can make queries less readable, especially when dealing with multiple tables or complex join conditions. Explicit joins (using INNER JOIN) make the intent of the query clearer.
2. Limited Join Types: Implicit joins are typically used for inner joins. If you need to perform different types of joins (e.g., left join, right join, full outer join), explicit joins provide a more versatile and standardized way to do so.
3. Portability: Some database systems may not support implicit joins, or their behavior may differ. Using explicit joins is more portable and works consistently across different database systems.

For these reasons, it's generally recommended to use explicit joins (e.g., INNER JOIN, LEFT JOIN, etc.) when working with multiple tables in SQL. They provide better clarity, flexibility, and compatibility across database systems. However, if you encounter implicit joins in existing code or have specific requirements, you can use them as long as you're aware of their limitations.