Filtering Records in Amazon Redshift Based on Timestamps and Country Order

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In this article, we will explore how to identify records in an Amazon Redshift table based on a specific timestamp order and country sequence. We will delve into the SQL query structure, window functions, and data manipulation techniques required to achieve this.

Background: Understanding Amazon Redshift and Window Functions

Amazon Redshift is a cloud-based data warehousing service that provides high-performance analytics capabilities. It uses a columnar storage engine, which allows for efficient query performance and data compression.

Window functions in SQL are used to perform calculations across rows that are related to the current row. In Amazon Redshift, window functions can be used with aggregate functions to calculate values over rows.

In this article, we will focus on using window functions to filter records based on timestamp order and country sequence.

Problem Statement

Suppose we have a table with a structure like the following:

+---------+-------+------------+--------+
| titleId | country | updateTime | value  |
+---------+-------+------------+--------+
| ID1    | US     | 2020-01-01 | someValueA|
| ID1    | US     | 2020-01-01 | someValueB|
| ID1    | IN     | 2020-01-04 | someValue |
| ID2    | ...    | ...        | ...    |
| ID3    | ...    | ...        | ...    |
+---------+-------+------------+--------+

We want to find three sets of records:

Records where ‘IN’ comes after ‘US’.
Records where ‘US’ comes after ‘IN’.
Records with only ‘IN’ entries and no other rows.

Solution Overview

To solve this problem, we will use Amazon Redshift window functions to calculate the number of ‘US’ and ‘IN’ records that come before each row.

We will then filter the results based on these calculated values.

Step 1: Calculate the Number of ‘US’ Records Before Each Row

SELECT t.*
FROM (SELECT t.*,
             SUM((country = 'US')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_us_following
      FROM t
     ) t;

This query calculates the number of ‘US’ records that come before each row for each titleid. The window function uses a row-by-row comparison to calculate this value.

Step 2: Calculate the Number of ‘IN’ Records Before Each Row

SELECT t.*
FROM (SELECT t.*,
             SUM((country = 'IN')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_in_following
      FROM t
     ) t;

This query calculates the number of ‘IN’ records that come before each row for each titleid. The window function uses a row-by-row comparison to calculate this value.

Step 3: Filter Records Based on Timestamp Order and Country Sequence

SELECT *
FROM (SELECT t.*,
             SUM((country = 'US')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_us_following,
             SUM((country = 'IN')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_in_following,
             SUM(country <> 'IN')::int) OVER (PARTITION BY titleid) AS non_nonind
      FROM t
     ) t;

WHERE country = 'IN' AND num_us_following > 0;

This query filters records where ‘IN’ comes after ‘US’. The WHERE clause uses the calculated values from previous steps to filter out rows that do not meet this condition.

SELECT *
FROM (SELECT t.*,
             SUM((country = 'US')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_us_following,
             SUM((country = 'IN')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_in_following,
             SUM(country <> 'IN')::int) OVER (PARTITION BY titleid) AS non_nonind
      FROM t
     ) t;

WHERE country = 'US' AND num_in_following > 0;

This query filters records where ‘US’ comes after ‘IN’. The WHERE clause uses the calculated values from previous steps to filter out rows that do not meet this condition.

SELECT *
FROM (SELECT t.*,
             SUM((country = 'US')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_us_following,
             SUM((country = 'IN')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_in_following,
             SUM(country <> 'IN')::int) OVER (PARTITION BY titleid) AS non_nonind
      FROM t
     ) t;

WHERE country = 'IN' AND non_nonind = 0;

This query filters records with only ‘IN’ entries and no other rows. The WHERE clause uses the calculated values from previous steps to filter out rows that do not meet this condition.

Step 4: Combine Results

SELECT *
FROM (
  SELECT *
  FROM (SELECT t.*,
             SUM((country = 'US')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_us_following
           FROM t
          ) t1
       WHERE t1.num_us_following > 0

  UNION ALL

  SELECT *
  FROM (SELECT t.*,
             SUM((country = 'US')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_us_following
           FROM t
          ) t1
       WHERE t1.num_us_following = 0

  UNION ALL

  SELECT *
  FROM (SELECT t.*,
             SUM((country = 'US')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_us_following
           FROM t
          ) t1
       WHERE t1.num_us_following > 0

  UNION ALL

  SELECT *
  FROM (SELECT t.*,
             SUM((country = 'IN')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_in_following
           FROM t
          ) t1
       WHERE t1.num_in_following > 0

  UNION ALL

  SELECT *
  FROM (SELECT t.*,
             SUM((country = 'IN')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_in_following
           FROM t
          ) t1
       WHERE t1.num_in_following = 0

  UNION ALL

  SELECT *
  FROM (SELECT t.*,
             SUM((country = 'IN')::int) OVER (PARTITION BY titleid ORDER BY updateTime ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING) AS num_in_following
           FROM t
          ) t1
       WHERE t1.num_in_following > 0
)
ORDER BY titleid, updateTime;

This query combines the results from previous steps using UNION ALL to create a single result set.

The final answer is:

+---------+-------+------------+--------+
| titleId | country | updateTime | value  |
+---------+-------+------------+--------+
| ID1    | IN     | 2020-01-04 | someValue|
| ...    | ...    | ...        | ...    |
+---------+-------+------------+--------+

Note that the actual results will depend on the data in your table.

I hope this helps! Let me know if you have any questions or need further clarification.

Last modified on 2024-04-26