Calculating Time Ranges Within a Specific Period: A SQL Solution

Calculating Time Ranges within a Specific Period

When working with date ranges, it can be challenging to determine if a specific date falls within a certain period. This problem arises in various applications, such as scheduling and reporting. In this article, we’ll explore ways to calculate time ranges within a specific period, including how to pick up dates from some range.

Introduction

In the given Stack Overflow question, a table is provided with records of consultants who have done aftercare activities for new candidates starting jobs. The task at hand is to build a report that compares if the aftercare activity was completed on time or not. To achieve this, we need to calculate the difference between the due date and the actual completion date.

Calculating Time Ranges

One approach to solving this problem is by using SQL queries. We’ll use an example with sample data to demonstrate how to pick up dates from some range.

Sample Data

Let’s create a table called consultant_activities with the following structure:

+-------------+---------------+-------------------+
| ConsultantID | CandidateID  | AfterCareDueDate |
+-------------+---------------+-------------------+
|           123 |             1 | 01/02/2019       |
|           123 |             1 | 20/02/2019       |
|           123 |             1 | 01/02/2019       |
|           123 |             1 | 07/02/2019       |
|           100 |             2 | 01/02/2019       |
|           100 |             2 | 20/02/2019       |
|           200 |             3 | 01/02/2019       |
+-------------+---------------+-------------------+

Calculating the Difference between Due Date and Actual Completion Date

To find out if an aftercare activity was completed on time or not, we need to calculate the difference between the due date and the actual completion date.

MIN(case when DESCRIPTION='Aftercare Pre Start' then DUEDATECONCAND end) AS DUEDATEPreStart,
 hin

This query uses the MIN function to return the smallest value in the specified column. In this case, it returns the earliest due date for each consultant.

Picking Up Dates from Some Range

Now that we have the earliest due date for each consultant, let’s calculate the time range within which the aftercare activity must be completed.

We can use the following SQL query to pick up dates from some range:

SELECT 
  ConsultantID,
  CandidateID,
  candidateNAME,
  AfterCareDueDate,
  (AfterCareDueDate - CURRENT_DATE) AS DaysUntilDueDate,
  (Current_Day() - DATE_TRUNC('week', CURRENT_DATE)) AS Weekends
FROM consultant_activities
WHERE 
  CURRENT_DATE + INTERVAL '3 day' <= AfterCareDueDate
  AND DAYOFWEEK(AfterCareDueDate) NOT IN ('6', '7')

This query returns the consultant ID, candidate name, aftercare due date, days until due date, and weekends within the specified period.

Explanation

The above SQL query works as follows:

CURRENT_DATE + INTERVAL '3 day' <= AfterCareDueDate: This part of the query checks if the current date plus three days is less than or equal to the aftercare due date.
AND DAYOFWEEK(AfterCareDueDate) NOT IN ('6', '7'): This part of the query excludes weekends (Saturdays and Sundays) from the calculation.

The (AfterCareDueDate - CURRENT_DATE) AS DaysUntilDueDate part calculates the number of days until the aftercare due date, while the (Current_Day() - DATE_TRUNC('week', CURRENT_DATE)) AS Weekends part calculates the number of weekends within the specified period.

Limitations

There are a few limitations to this approach:

The query assumes that the AfterCareDueDate is always on or before the 3rd day from the current date.
If there are multiple due dates for the same consultant, it will only consider the earliest one in the calculation.

To address these limitations, we can modify the query to include additional checks and considerations:

Handling Multiple Due Dates

We can use the ROW_NUMBER function to assign a ranking to each row based on the AfterCareDueDate. Then, we can select the top N rows for each consultant ID.

WITH RankedActivities AS (
  SELECT 
    ConsultantID,
    CandidateID,
    AfterCareDueDate,
    ROW_NUMBER() OVER (PARTITION BY ConsultantID ORDER BY AfterCareDueDate) AS RowNumber
  FROM consultant_activities
)
SELECT 
  ConsultantID,
  CandidateID,
  candidateNAME,
  AfterCareDueDate,
  DaysUntilDueDate,
  Weekends
FROM (
  SELECT 
    ConsultantID,
    CandidateID,
    candidateNAME,
    AfterCareDueDate,
    (AfterCareDueDate - CURRENT_DATE) AS DaysUntilDueDate,
    (Current_Day() - DATE_TRUNC('week', CURRENT_DATE)) AS Weekends,
    ROW_NUMBER() OVER (PARTITION BY ConsultantID ORDER BY AfterCareDueDate) AS RowNumber
  FROM consultant_activities
) AS Subquery
WHERE 
  ConsultantID IN (
    SELECT ConsultantID FROM RankedActivities WHERE RowNumber = 1
  )
  AND CURRENT_DATE + INTERVAL '3 day' <= AfterCareDueDate
  AND DAYOFWEEK(AfterCareDueDate) NOT IN ('6', '7')

Handling Edge Cases

We can use additional checks and considerations to handle edge cases such as:

If the AfterCareDueDate is on or before the current date, we should exclude it from the calculation.
If there are no aftercare activities within the specified period for a particular consultant ID, we should return an empty result set.

By addressing these limitations and edge cases, we can develop a more robust solution that accurately calculates time ranges within specific periods.

Last modified on 2024-02-15