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Problem solution · SQL

Report Contiguous Dates

Report Contiguous Dates: 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
32 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 Report Contiguous Dates, 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

  • 32 lines of SQL from the credited upstream file 1225.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 codeReport Contiguous Dates · SQLSQL
Use this to learn the idea, then write your own version.
WITH  RankedDatesPerState AS (    SELECT      'failed' AS state,      fail_date AS `date`,      RANK() OVER(ORDER BY fail_date) AS rank_per_state    FROM Failed    WHERE fail_date BETWEEN '2019-01-01' AND '2019-12-31'    UNION ALL    SELECT      'succeeded' AS state,      success_date AS `date`,      RANK() OVER(ORDER BY success_date) AS rank_per_state    FROM Succeeded    WHERE success_date BETWEEN '2019-01-01' AND '2019-12-31'  ),  RankedDates AS (    SELECT      state,      `date`,      rank_per_state,      RANK() OVER(ORDER BY `date`) AS `rank`    FROM RankedDatesPerState  )SELECT  state AS period_state,  MIN(`date`) AS start_date,  MAX(`date`) AS end_dateFROM RankedDatesGROUP BY state, (`rank` - rank_per_state)ORDER BY start_date

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