Projection operation in DBMS Theory - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the SQL query to select only the 'name' column from the 'students' table.

DBMS Theory

SELECT [1] FROM students;

Drag options to blanks, or click blank then click option'

AWHERE

B*

Cstudents

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' selects all columns, not just 'name'.

Using table name instead of column name after SELECT.

The projection operation in SQL is done using the SELECT statement with the column names you want to retrieve. Here, selecting 'name' returns only that column.

2fill in blank

medium

Complete the SQL query to select the 'id' and 'email' columns from the 'users' table.

DBMS Theory

SELECT id, [1] FROM users;

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Apassword

Bemail

Caddress

Dphone

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting unrelated columns like 'password' or 'phone'.

Forgetting to separate columns with commas.

To project multiple columns, list them separated by commas after SELECT. Here, 'email' is the second column to select.

3fill in blank

hard

Fix the error in the SQL query to select the 'title' column from the 'books' table.

DBMS Theory

SELECT [1] FROM books

Drag options to blanks, or click blank then click option'

Atitle;

Btitle

C*

Dbooks

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the semicolon at the end of the query.

Using table name instead of column name after SELECT.

SQL statements must end with a semicolon. Adding ';' after 'title' fixes the syntax error.

4fill in blank

hard

Fill both blanks to select the 'first_name' and 'last_name' columns from the 'employees' table.

DBMS Theory

SELECT [1], [2] FROM employees;

Drag options to blanks, or click blank then click option'

Afirst_name

Bsalary

Clast_name

Ddepartment

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting columns unrelated to names.

Forgetting the comma between column names.

To project multiple columns, list their names separated by commas after SELECT. Here, 'first_name' and 'last_name' are the correct columns.

5fill in blank

hard

Fill all three blanks to select the uppercase 'city' name, the 'population', and only cities with population greater than 100000 from the 'cities' table.

DBMS Theory

SELECT [1](city) AS city_upper, [2] FROM cities WHERE population [3] 100000;

Drag options to blanks, or click blank then click option'

AUPPER

Bpopulation

C>

Dcity

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase function names or missing parentheses.

Selecting wrong columns or using wrong comparison operators.

The UPPER function converts city names to uppercase. We select 'population' as the second column. The WHERE clause filters cities with population greater than 100000 using '>'.