Working Process of Merge Join
Below are the mentioned steps of the working of Merge Join.
Step 1 – Precondition: The tables to be joined are taken care of at the be part of key columns. If the tables are not already sorted, they are taken care of earlier than the merge operation starts to evolve.
Step 2 – Initialization: Two hints (or cursors) are initialized at the start of every desk.
Step 3 – Traversal: The algorithm iteratively compares the part of key values of the rows pointed to by using the cursors in both tables.
- If the join key values suit, the rows from each table are combined to form a new row in the result set, and each hint is moved to the next row in their respective tables.
- If the part of the key cost within the first desk is smaller, the pointer inside the first desk moves to the next row.
- If the part of the key fee inside the 2d desk is smaller, the pointer in the second desk moves to the following row.
Step 4 – Termination: This process is maintained until one or both of the tables are entirely traversed.
Example
Let’s dive right into a greater example to demonstrate how merge joins work in a practical situation. Suppose we have tables, Orders, and Customers, and we need to join them based totally on a not-unusual column, CustomerID, to list orders at the side of customer facts. For simplicity, assume each tables are already taken care of on CustomerID.
Tables Before Join
Customers Table
|
CustomerID |
Name |
|---|---|
|
1 |
John |
|
2 |
Bob |
|
3 |
Alice |
Orders Table
|
OrderID |
CustomerID |
Product |
|---|---|---|
|
101 |
1 |
Apples |
|
102 |
2 |
Bananas |
|
103 |
1 |
Cherries |
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.