How to Efficiently Retrieve Last Month's Records from a SQL Server Table?

Retrieving Last Month's Records in SQL Server

Problem:

Obtain the records from the database table [member] that fall within the previous month, based on the date_created field.

Solution:

To efficiently and accurately retrieve last month's records, we need to avoid certain pitfalls and employ the following approach:

1. Use Exclusive Range Filtering:

   Instead of using inclusive ranges (e.g., BETWEEN operator), use exclusive range filtering with the > and < operators. This ensures that records from both the first and last day of the month are included.

2. Calculate Month Boundaries:

   Derive the start of the previous month and the start of the current month using appropriate date functions. This avoids potential issues caused by inclusive upper-bound ranges.

   • Start of Previous Month: DATEADD(month, -1, @startOfCurrentMonth)
   • Start of Current Month: DATEADD(month, DATEDIFF(month, 0, CURRENT_TIMESTAMP), 0)

3. Sample Query:

   DECLARE @startOfCurrentMonth DATETIME
   SET @startOfCurrentMonth = DATEADD(month, DATEDIFF(month, 0, CURRENT_TIMESTAMP), 0)
   
   SELECT *
   FROM Member
   WHERE date_created >= DATEADD(month, -1, @startOfCurrentMonth)
     AND date_created < @startOfCurrentMonth
   
   

This approach ensures that indices are used, data corruption is prevented, and the correct records are retrieved within the specified timeframe.

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