Projection operation in DBMS Theory - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the projection operation in a database?

Projection is a database operation that selects specific columns from a table, creating a new table with only those columns.

beginner

How does projection differ from selection in databases?

Projection chooses columns (attributes), while selection chooses rows (records) based on conditions.

intermediate

What happens if you project the same column multiple times?

The result will include that column only once; duplicates are removed in projection.

beginner

Why is projection useful in real-life database queries?

Projection helps to retrieve only needed information, reducing data size and improving query speed.

intermediate

Can projection change the number of rows in the result?

No, projection only changes columns; the number of rows stays the same unless duplicate rows are removed.

What does the projection operation do in a database?

A Selects specific rows from a table

B Joins two tables

C Deletes rows from a table

D Selects specific columns from a table

Projection selects specific columns (attributes) from a table.

Which of the following is true about projection?

A It selects specific columns from a table

B It selects specific rows based on conditions

C It changes the order of rows

D It removes duplicate rows automatically

Projection selects specific columns; it does not select rows or change order.

If you project columns 'Name' and 'Age' from a table, what will the result contain?

A Both 'Name' and 'Age' columns

B Only the 'Age' column

C Only the 'Name' column

D All columns except 'Name' and 'Age'

Projection returns only the specified columns, here 'Name' and 'Age'.

Does projection affect the number of rows in the output?

A Yes, it always reduces rows

B No, it only changes columns

C Yes, it duplicates rows

D Yes, it deletes rows randomly

Projection changes columns but keeps the same rows unless duplicate rows are removed.

Which operation would you use to get only the 'Email' column from a user table?

A Selection

B Join

C Projection

D Union

Projection is used to select specific columns like 'Email'.

Explain the projection operation and how it is used in databases.

Think about choosing only certain pieces of information from a table.

Describe the difference between projection and selection operations in a database.

One picks columns, the other picks rows.