Relational model mental model in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the SQL query to select all columns from the table named 'employees'.

SQL

SELECT [1] FROM employees;

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ACOLUMNS

BALL

CEVERY

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like ALL or COLUMNS instead of the symbol *.

Forgetting to specify columns or using invalid keywords.

In SQL, * means select all columns from the table.

2fill in blank

medium

Complete the SQL query to get only the distinct department names from the 'departments' table.

SQL

SELECT [1] department_name FROM departments;

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ADISTINCT

BONLY

CSINGLE

DUNIQUE

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNIQUE instead of DISTINCT in SELECT statements.

Using ONLY or SINGLE which are not valid SQL keywords here.

The keyword DISTINCT returns unique values in SQL.

3fill in blank

hard

Fix the error in the SQL query to count the number of employees in each department.

SQL

SELECT department_id, COUNT([1]) FROM employees GROUP BY department_id;

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Aemployee_id

B*

Cdepartment_id

Dname

Attempts:

3 left

💡 Hint

Common Mistakes

Counting a specific column that might have NULLs, causing wrong counts.

Using department_id inside COUNT() which counts the group key, not rows.

Using COUNT(*) counts all rows per group, which is the correct way to count employees.

4fill in blank

hard

Fill both blanks to create a query that finds employees with salary greater than 50000.

SQL

SELECT * FROM employees WHERE salary [1] [2];

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A>

B50000

C<

D100000

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator instead of greater than.

Using wrong salary values.

The condition salary > 50000 filters employees earning more than 50000.

5fill in blank

hard

Fill all three blanks to create a query that lists employee names and their department names by joining 'employees' and 'departments' tables.

SQL

SELECT e.name AS employee_name, d.name AS department_name FROM employees e [1] departments d ON e.[2] = d.[3];

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

AJOIN

Bdepartment_id

DLEFT

Attempts:

3 left

💡 Hint

Common Mistakes

Using LEFT instead of JOIN without ON clause.

Using wrong column names for joining.

Use JOIN to combine tables on matching department_id columns.