Create a Session Bar Chart - Practice Coding Problems

Create a Session Bar Chart - Problem

Database Easy

Given a Sessions table containing user session data, create a bar chart showing session duration distribution across predefined time bins.

You need to categorize each session into one of four bins based on duration (in seconds):

[0-5) - Sessions lasting 0 to 4 minutes
[5-10) - Sessions lasting 5 to 9 minutes
[10-15) - Sessions lasting 10 to 14 minutes
15 or more - Sessions lasting 15 minutes or longer

Return the count of sessions for each bin in the format (bin, total). The result can be returned in any order.

Table Schema

Sessions

Column Name	Type	Description
`session_id` PK	int	Unique identifier for each session
`duration`	int	Session duration in seconds

Primary Key: session_id

Note: Each row represents one user session with its duration in seconds

Input & Output

Example 1 — Mixed Duration Sessions

Input Table:

session_id	duration
1	20
2	399
3	462
4	843
5	1000

Output:

bin	total
[0-5>	1
[5-10>	2
[10-15>	1
15 or more	1

💡 Note:

Sessions are categorized by duration: 20 seconds (0-5 min), 399 and 462 seconds (5-10 min), 843 seconds (10-15 min), and 1000 seconds (15+ min). Each bin gets counted accordingly.

Example 2 — Edge Case Boundaries

Input Table:

session_id	duration
1	299
2	300
3	599
4	600

Output:

bin	total
[0-5>	1
[5-10>	2
[10-15>	1

💡 Note:

Tests boundary conditions: 299 seconds is just under 5 minutes ([0-5>), while 300 seconds exactly equals 5 minutes ([5-10>). Similarly, 599 seconds is under 10 minutes, but 600 seconds equals exactly 10 minutes.

Example 3 — Single Bin Distribution

Input Table:

session_id	duration
1	45
2	200
3	250

Output:

bin	total
[0-5>	3

💡 Note:

All sessions fall within the first bin (under 5 minutes), so only one row is returned. Empty bins are not included in the result.

Constraints

1 ≤ session_id ≤ 10^5
1 ≤ duration ≤ 10^6
Duration is measured in seconds

Visualization

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Understanding the Visualization

Input Data

Sessions with duration in seconds

Categorization

CASE WHEN assigns bins based on duration ranges

Aggregation

GROUP BY bins and COUNT sessions

Key Takeaway

🎯 Key Insight: CASE WHEN statements are perfect for creating custom data bins and categories in SQL

Asked in

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Use CASE WHEN statements to categorize session durations into predefined time bins (0-5, 5-10, 10-15, 15+ minutes), then GROUP BY the bins and COUNT(*) sessions in each category.

Table Schema

Sessions

Column Name	Type	Description
`session_id` PK	int	Unique identifier for each session
`duration`	int	Session duration in seconds

Primary Key: session_id

Note: Each row represents one user session with its duration in seconds

Common Approaches

Approach	Time	Space	Notes
✓ CASE WHEN Binning	O(n)	O(1)	Use CASE WHEN to categorize durations into bins and COUNT each category

CASE WHEN Binning — Algorithm Steps

Step 1: Convert duration from seconds to minutes using division by 60
Step 2: Use CASE WHEN to categorize each session into appropriate bin
Step 3: GROUP BY bin categories and COUNT sessions in each

Visualization

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Step-by-Step Walkthrough

Convert

Check duration ranges

Categorize

Assign to bins with CASE

Count

GROUP BY and COUNT

Code -

solution.c — C

Time & Space Complexity

Time Complexity

⏱️

O(n)

Single pass through all sessions

✓ Linear Growth

Space Complexity

O(1)

Fixed number of output bins

✓ Linear Space

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Table Schema

Input & Output

Constraints

Visualization

Related Problems

Table Schema

Common Approaches

CASE WHEN Binning — Algorithm Steps

Visualization

Code -

Time & Space Complexity

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