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Problem solution · SQL

Viewers Turned Streamers

Viewers Turned Streamers: a SQL solution using relational aggregation. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Relational aggregation
Source
walkccc LeetCode Solutions
Length
23 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Relational aggregation

For Viewers Turned Streamers, the query transforms and combines relational rows, then filters or aggregates them into the requested result.

  1. Identify the source rows and join keys.
  2. Apply filters before aggregation when possible.
  3. Group, rank, or project the final columns required by the result.

Code notes

  • 23 lines of SQL from the credited upstream file 2995.sql.
  • The implementation keeps its working state in language-native values and containers.
  • No explicit loop blocks detected.

Complexity

Review join cardinality, grouping keys, and available indexes when estimating query cost.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeViewers Turned Streamers · SQLSQL
Use this to learn the idea, then write your own version.
WITH  FirstSessions AS (    SELECT      user_id,      session_type,      RANK() OVER(PARTITION BY user_id ORDER BY session_start) AS session_rank    FROM Sessions  ),  ViewerFirst AS (    SELECT user_id    FROM FirstSessions    WHERE session_rank = 1 AND session_type = 'Viewer'  )SELECT  Sessions.user_id,  COUNT(*) AS sessions_countFROM SessionsINNER JOIN ViewerFirst  USING (user_id)WHERE Sessions.session_type = 'Streamer'GROUP BY 1ORDER BY sessions_count DESC, Sessions.user_id DESC;

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