Sensor Online Periods

SQL practice question · Hard · Gaps & Islands · Amazon

Warehouse temperature sensors should report every 5 minutes. Identical (sensor_id, reading_ts) rows are duplicates. Consecutive readings at most 15 minutes apart belong to the same ONLINE period; a gap of more than 15 minutes starts a new period. Return `sensor_id`, `period_start`, `period_end`, `readings` (distinct timestamps in the period). Order by `sensor_id`, `period_start`.

Table: fc_sensor_readings

Schema of fc_sensor_readings
ColumnType
sensor_idTEXT
reading_tsTIMESTAMP
temp_cREAL
Sample rows of fc_sensor_readings
sensor_idreading_tstemp_c
S12026-11-01 00:00:004.1
S12026-11-01 00:05:004
S12026-11-01 00:10:004.2
S12026-11-01 00:40:004.4
S12026-11-01 00:45:004.3
S12026-11-01 01:30:004.1
S22026-11-01 00:00:00-18
S22026-11-01 00:15:00-18.2
Expected output on the sample data
sensor_idperiod_startperiod_endreadings
S12026-11-01 00:00:002026-11-01 00:10:003
S12026-11-01 00:40:002026-11-01 00:45:002
S12026-11-01 01:30:002026-11-01 01:30:001
S22026-11-01 00:00:002026-11-01 00:15:002
S22026-11-01 00:31:002026-11-01 00:31:001

Solve it in the live editor on this page — run on sample data, then submit against hidden tests.

‹ App Store Year-over-Year Revenue by Category · Riders Taking a Second Trip Within 7 Days ›

T
Tech Town
Log InSign Up Free
Home SQL Python DSA Power BI Snowflake Databricks Spark Gen AI Practice Problems Contest Question Asked in Interview Blog
SQL Interview Practice

Company-wise SQL questions

{{ totalCount }} questions in the style asked at Amazon, Microsoft, Google, Meta, Flipkart and more — {{ hardPct }}% Hard. Write SQL in a real database engine in your browser, run it on sample data, then evaluate against hidden tests.

🏆 Weekly SQL Contest
{{ totalCount }}
Questions
{{ companyCount }}
Companies
{{ prog.total.solved }}
Solved
Bookmark Question Companies Difficulty Category Status
{{ r.n }} - {{ r.title }} {{ c }} {{ r.difficulty }} {{ r.category }} {{ r.statusIcon }}
No questions match these filters.
Showing {{ rangeLabel }} of {{ filteredCount }}

Company tags show where this type of question is commonly reported in interviews. Questions, data and solutions are written by TechTown.
← All questions

{{ cur.n }} - {{ cur.title }}

🏆 Contest {{ contestWeek }}
{{ cur.catLabel }} {{ cur.diffLabel }} {{ c }}
Embed this questionPaste on a blog, course page or LMS. Free to use — educator guide 
{{ embedCode }}

{{ cur.statement }}

Table: {{ tb.name }}
ColumnType {{ c.name }}{{ c.type }}
{{ h }} {{ v.text }}
Expected output on the sample data:
{{ h }} {{ v.text }}
  • {{ h }}

No submissions yet. Press Evaluate to submit your query.
{{ s.verdict }} {{ s.meta }}
The solution unlocks after you solve this question or after 3 evaluations that didn't pass ({{ failCount }}/3 so far). Trying first is the fastest way to learn. 
{{ solutionSql }}
  1. {{ e }}
⏱ {{ timerLabel }}
{{ fnHelpTitle }}
{{ fnHelpText }}
Writing {{ dialectName }} · Ctrl/Cmd + Enter runs the query · Tab indents · your code is saved automatically
Output {{ out.status }}
  • {{ w }}
    •
{{ out.verdict }}
{{ out.detail }}
 
{{ out.error }}
Expected (sample data)
{{ h }}{{ v.text }}
Your output (sample data)
{{ h }}{{ v.text }}
{{ h }} {{ v.text }}
Run your query to see the result here.
🔒

To Track Your Progress, Log In / Sign Up

You have solved your 3 free questions — nice work! Log in (free) to unlock all 150 questions, keep your streak and appear on the leaderboard.

Sign Up Free Log In