Question

What is the cost of selection operation, when the index scan method is used? Explain with the help of an example. Explain the cost of Join operation when Merge-Join method is used.

13 Sep 2024
Answer :
Word Count : 868

In the context of Database Management Systems (DBMS), both the selection operation and the join operation have distinct cost implications depending on the method used. Here’s a detailed explanation of the costs associated with these operations, focusing on the index scan method for selection and the merge-join method for joins.

### Cost of Selection Operation with Index Scan

Selection Operation:
The selection operation involves retrieving rows from a table that satisfy a specific condition. For example, if we want to retrieve all employees with a salary greater than $50,000 from an `Employees` table, the selection operation is applied to this condition.

Index Scan Method:
When using an index scan for the selection operation, the cost depends on several factors, including the type of index used (e.g., B-tree, hash), the index's selectivity, and the number of records.

Index Scan Cost Calculation:

1. Index Structure Cost:
   - B-Tree Index: For a B-tree index, the cost of traversing the index is proportional to the height of the tree. The height of a _____ _________ ___ _______ ________ _______.
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