Efficiently generate T-SQL date sequence
In various data processing tasks, it is often necessary to create a date result set within a specified range. For example, you need to generate a list of dates between a start date and an end date.
Loop-based method
A common way to generate a date sequence is to use a WHILE loop, as shown below:
-- 此方法效率低下,尤其是在处理大范围日期时。
However, this approach is inefficient, especially when dealing with large ranges of dates.
Use a number table
A more efficient solution is to utilize the MASTER.DBO.SPT_VALUES table, which provides a sequence of numbers from 1 to 2047. By using this table with the DATETADD function, you can generate a set of dates within a specified range using the following query:
DECLARE @dt datetime, @dtEnd datetime SET @dt = GETDATE() SET @dtEnd = DATEADD(DAY, 100, @dt) SELECT DATETADD(DAY, number, @dt) FROM (SELECT number FROM MASTER.DBO.SPT_VALUES WHERE TYPE = 'P') AS n WHERE DATETADD(DAY, number, @dt) < @dtEnd
This query generates a result set of dates from @dt to @dtEnd-1.
SQL Server 2008 and later features
SQL Server 2008 introduced the GENERATE_SERIES function, which can generate numeric sequences. This function can be used to generate a date result set as follows (SQL Server 2008 or later):
DECLARE @Start datetime, @End datetime SET @Start = '2024-01-01' SET @End = '2024-12-31' SELECT DATEADD(DAY, n, @Start) FROM (SELECT TOP (DATEDIFF(DAY, @Start, @End) + 1) n = ROW_NUMBER() OVER (ORDER BY object_id)) AS SubTable ORDER BY n
This query returns a result set of dates from @Start to @End (inclusive).
By using these techniques, you can efficiently generate result sets of increasing dates within a user-defined range in T-SQL.
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