Step-by-Step Merge Join Process

Below are the mentioned steps in the process of Merge Join in DBMS.

1. Initialization

Start with the first row of each table.

Customers: Point to Alice (CustomerID = 1).
Orders: Point to OrderID 101 (CustomerID = 1).

2. Compare and Advance

Since the CustomerID matches (1 = 1), join these rows and move to the next rows in both tables.
Result Set After Step 2:

CustomerID	Name	OrderID	Product
1	John	101	Apples

3. Next Comparison

Now, we compare Alice (CustomerID = 1) in Customers with the next Projection Operation in DBMS in Orders (OrderID = 103, CustomerID = 1).
Since the CustomerID still matches, join these rows.
Result Set After Step 3:

CustomerID	Name	OrderID	Product
1	John	101	Apple
2	John	103	Cherries

4. Move to Bob and Bananas

Move to the next row in Customers (Bob, CustomerID = 2) and the next row in Orders (OrderID = 102, CustomerID = 2).
Match and join these rows.
Result Set After Step 4:

CustomerID	Name	OrderID	Product
1	John	101	Apple
1	John	103	Cherries
2	Bob	102	Bananas

5. End of Join

Since there are no more orders for Charlie (CustomerID = 3) and no more orders to process, the join operation is complete.

Final Result

CustomerID	Name	OrderID	Product
1	John	101	Apples
1	John	103	Cherries
2	Bob	102	Bananas

The merge join worked correctly here due to the fact:

Both tables have been pre-looked after on the be part of column (CustomerID).
The set of rules made a unmarried bypass through each table, evaluating and advancing recommendations based totally on the kind order.

Merge Join in DBMS

Merge be part of is a hard and fast-based be part of operation used in database control systems (DBMS) to mix rows from or extra tables based on an associated column among them. It is mainly efficient whilst the tables involved are large and while they are each sorted on the be a part of the key, which is the column or set of columns used for the join. Here’s an outline of the way merge is a part of works, its benefits, and when it is best used.