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.