SQL Showing Every Hour of Every Day

In this article, we’ll explore a common problem in data analysis: how to show every hour of every day for a given dataset. We’ll dive into the technical details of SQL and examine various approaches to solve this issue.

Understanding the Problem

The question at hand involves taking a dataset that contains patient arrival and departure information, and breaking it down into hourly increments for each day. This allows us to analyze patient census by hour, providing valuable insights into hospital operations.

However, when we attempt to split out every day into every hour using SQL, we encounter an unexpected issue. Instead of producing 24 hours of data per day, the query produces 25 hours of data per day. This discrepancy arises due to the way we’re handling date calculations and comparisons.

Approach 1: Using CROSS APPLY

In this section, we’ll examine the original code snippet provided by the questioner. The approach employs a CROSS APPLY operation to split out each row into multiple rows based on the hour value.

SELECT
    Date = CAST(D AS DATE)
    ,Hour = DATEPART(HOUR, D)
    ,A.pt_id
    ,cendate
    ,locationid
    ,[room-bed]
    ,startdatetime
    ,enddatetime
    ,minutes
    ,DayOfWeek
    ,WeekInt
    ,MyStartMinutes = 0
    ,MyEndMinutes = 0
INTO #Temporary2
FROM #Temporary A
CROSS APPLY
(
    SELECT TOP ( ABS(DATEDIFF(HOUR, A.startdatetime, A.enddatetime) + 1))
        D = DATEADD(HOUR, -1 + ROW_NUMBER() OVER ( ORDER BY ( SELECT NULL )), A.startdatetime)
        ,A.pt_id
    FROM master..spt_values n1
        ,master..spt_values n2
) B
WHERE A.pt_id = B.pt_id

Approach 2: Modifying the CROSS APPLY Operation

The answer provided by the questioner suggests modifying the CROSS APPLY operation to include the primary key (pt_id) from the original table. This ensures that we’re only processing rows with matching IDs.

SELECT
    Date = CAST(D AS DATE)
    ,Hour = DATEPART(HOUR, D)
    ,A.pt_id
    ,cendate
    ,locationid
    ,[room-bed]
    ,startdatetime
    ,enddatetime
    ,minutes
    ,DayOfWeek
    ,WeekInt
    ,MyStartMinutes = 0
    ,MyEndMinutes = 0
INTO #Temporary2
FROM #Temporary A
CROSS APPLY
(
    SELECT TOP ( ABS(DATEDIFF(HOUR, A.startdatetime, A.enddatetime) + 1))
        D = DATEADD(HOUR, -1 + ROW_NUMBER() OVER ( ORDER BY ( SELECT NULL )), A.startdatetime)
        ,A.pt_id
    FROM master..spt_values n1
        ,master..spt_values n2
    WHERE A.pt_id = B.pt_id
) B

Approach 3: Using a Different Query Structure

Alternatively, we can use a different query structure to achieve the desired result. This approach involves using a single UNION ALL statement to combine rows from multiple rows.

SELECT 
    DATEADD(HOUR, -1, startdatetime) AS Date
    ,DATEPART(HOUR, DATEADD(HOUR, -1, startdatetime)) AS Hour
    ,pt_id
    ,cendate
    ,locationid
    ,[room-bed]
    ,startdatetime
    ,enddatetime
    ,minutes
    ,DayOfWeek
    ,WeekInt
    ,MyStartMinutes = 0
    ,MyEndMinutes = 0
FROM dbo.Census
UNION ALL
SELECT 
    DATEADD(HOUR, -1, enddatetime) AS Date
    ,DATEPART(HOUR, DATEADD(HOUR, -1, enddatetime)) AS Hour
    ,pt_id
    ,cendate
    ,locationid
    ,[room-bed]
    ,startdatetime
    ,enddatetime
    ,minutes
    ,DayOfWeek
    ,WeekInt
    ,MyStartMinutes = 0
    ,MyEndMinutes = 0
FROM dbo.Census

Conclusion

In conclusion, we’ve explored several approaches to solve the problem of showing every hour of every day for a given dataset. By modifying the CROSS APPLY operation and using a different query structure, we can produce accurate results.

When working with date calculations and comparisons in SQL, it’s essential to consider the nuances of each approach and choose the one that best fits your needs.

Final Answer

To solve this problem, you can use any of the approaches mentioned above. However, I recommend using Approach 2: Modifying the CROSS APPLY Operation, as it provides a more robust solution.

SELECT
    Date = CAST(D AS DATE)
    ,Hour = DATEPART(HOUR, D)
    ,A.pt_id
    ,cendate
    ,locationid
    ,[room-bed]
    ,startdatetime
    ,enddatetime
    ,minutes
    ,DayOfWeek
    ,WeekInt
    ,MyStartMinutes = 0
    ,MyEndMinutes = 0
INTO #Temporary2
FROM #Temporary A
CROSS APPLY
(
    SELECT TOP ( ABS(DATEDIFF(HOUR, A.startdatetime, A.enddatetime) + 1))
        D = DATEADD(HOUR, -1 + ROW_NUMBER() OVER ( ORDER BY ( SELECT NULL )), A.startdatetime)
        ,A.pt_id
    FROM master..spt_values n1
        ,master..spt_values n2
    WHERE A.pt_id = B.pt_id
) B

Last modified on 2024-09-01