Generating a Date Series in T-SQL
This article demonstrates efficient techniques for creating a result set containing a sequence of dates within a given range using T-SQL. We'll explore methods for generating this date series, focusing on optimized approaches.
Defining the Date Range
Let's establish our start and end dates:
DECLARE @StartDate datetime = 'Mar 1 2009', @EndDate datetime = 'Aug 1 2009'
A Loop-Based Approach (Less Efficient)
A straightforward, but less efficient, method utilizes a WHILE
loop:
DECLARE @currentDate datetime SET @currentDate = @StartDate WHILE @currentDate <= @EndDate BEGIN SELECT @currentDate SET @currentDate = DATEADD(day, 1, @currentDate) END
This iterative approach works, but it can be slow for large date ranges.
Optimized Approach using spt_values
(SQL Server 2005 and later)
For improved performance, especially with wider date ranges, leverage the spt_values
system table (available in SQL Server 2005 and later versions):
DECLARE @StartDate datetime, @EndDate datetime; SET @StartDate = GETDATE(); SET @EndDate = DATEADD(day, 100, @StartDate); SELECT DATEADD(day, number, @StartDate) AS DateValue FROM master..spt_values WHERE type = 'P' AND DATEADD(day, number, @StartDate) <= @EndDate;
This query efficiently generates the date series by adding sequential numbers from spt_values
to the start date and filtering to include only dates within the specified range. This method is significantly faster than the loop-based approach for larger datasets. The master..spt_values
table provides a readily available sequence of numbers, making it ideal for this task.
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