Difference Between Selection And Projection In Dbms
distinguishing selection and projection operations in DBMS
Difference Between Selection And Projection In Dbms
In database management systems (DBMS), selection and projection are two key operations used in querying databases. Selection involves extracting specific rows or tuples from a table based on a specified criteria or condition, such as retrieving all customer records where the age is greater than 30. On the other hand, projection involves extracting specific columns or attributes from a table, resulting in a subset of columns being retrieved while keeping all rows intact. For example, a projection operation may involve selecting only the customer names and addresses from a table of customer records. In summary, selection is used to filter rows based on conditions, while projection is used to filter columns, helping to tailor query results to specific requirements.
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1 - Selection in DBMS:
Selection is a query operation that retrieves specific rows or records from a database based on certain criteria or conditions.
It uses the WHERE clause to filter out the data that meets the specified criteria.
For example, selecting all customers who are from a specific city like “New York” from a customer database.
2) Projection in DBMS:
Projection is a query operation that retrieves specific columns or attributes from a database table while discarding the rest of the columns.
It helps in viewing only the required data attributes, making the output more focused and concise.
For example, projecting only the ‘name’ and ‘age’ columns from a ‘student’ table.
3) Difference in Purpose:
Selection is used to filter rows based on specific conditions, while projection is used to select specific columns for display.
4) Data Retrieval:
Selection retrieves complete rows of data based on certain conditions, whereas projection retrieves specific columns from these rows.
5) Syntax:
Selection is accomplished using the WHERE clause in SQL, while projection is achieved by specifying the desired columns in the SELECT statement.
6) Output:
The output of selection will have all columns for the selected rows that meet the conditions, while projection will display only the specified columns.
7) Characteristic:
Selection is primarily concerned with filtering data, whereas projection is focused on selecting specific attributes.
8) Flexibility:
Selection allows for complex conditions to filter rows, while projection gives flexibility in choosing desired columns for display.
9) Performance:
Selection may involve processing more data depending on the filter conditions, while projection can help improve performance by fetching only the necessary columns.
10) Teaching Tip:
To help students understand the difference between selection and projection in DBMS, you can provide hands on exercises with SQL queries that involve both operations. This practical training will reinforce their understanding and skills in querying databases effectively.
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