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Learn how to effectively write a WHERE clause in SQL to find patients who were in a hospital during a specific date range, even if they were admitted before or discharged after that range.
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How to Use SQL to Filter Dates within a Date Range Properly

When working with databases, particularly in healthcare, it is common to analyze patient records over specific time periods. A frequent challenge arises when you need to retrieve data for patients who were present in a hospital during a defined date range, even if their admit or discharge date falls outside that range. This guide addresses the specific case of retrieving patient information for those who were admitted before and discharged after a specific month.

The Problem Explained

Imagine you are tasked with pulling a list of all patients who were in Hospital 1 during the month of May 2021. Your data includes admit dates and discharge dates, which may not neatly fall within the boundaries of the month you are interested in. You might have patients with:

An admit date before May and a discharge date within May.

An admit date within May and a discharge date after May.

An admit date before May and a discharge date after May.

Your goal is to create a query that captures all patients who were present in the hospital at any time during May, allowing you to analyze patient census effectively for any date within that month.

The initial attempt to solve this issue might commonly involve using a BETWEEN clause. However, as you discovered, this method fails to capture patients like those who were admitted before May and discharged after May, leaving critical data uncollected.

Example Dataset

For clarity, let’s look at the following patient records:

PatientAdmit_DateDisch_Date14/5/20215/20/202125/6/20215/10/202134/10/20214/22/202144/19/20217/5/202156/1/20216/7/2021From this dataset, you want to identify all patients who were present in the hospital any time during May.

The Solution

The correct approach to ensure you're capturing all relevant patients involves specifying conditions for both admit and discharge dates in your SQL WHERE clause. You want to include anyone who:

Was admitted prior to the end of the month (May 31, 2021).

Discharged after the start of the month (May 1, 2021).

SQL Query Example

Here's how you can structure your SQL WHERE clause to achieve this:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Query

Admit_Date = '2021-05-31': This condition ensures that any patient admitted on or before May 31 will be included.

Disch_Date = '2021-05-01': This part of the clause captures patients who were still admitted on or after May 1, regardless of their admit date.

By combining these two conditions, you effectively capture all relevant patients based on their hospital stay during May, even if their admissions or discharges happened outside of that month, like in the following cases:

Patient 1 was admitted on April 5th and discharged on May 20th.

Patient 2 was admitted and discharged in May.

Patient 4 was admitted before May and discharged after May.

Conclusion

Retrieving accurate patient data within a specific date range can be challenging, especially when using standard filtering techniques. However, by understanding how to structure your SQL WHERE clauses correctly, you can ensure comprehensive data retrieval. With the query shared above, you should now be able to pull relevant patient data for any date range, enhancing your analyses and reports.

| Analyze patient admissions accurately with the right SQL! |