How to Create a 100-Year Calendar Table in SQL for Efficient Date-Related Queries?

Create a calendar table covering 100 years in SQL

Suppose you have a data set containing a large number of dates and need to extract specific information, such as the day of the year or the number of weeks. Creating a calendar table allows you to easily retrieve this information by connecting your data with the calendar table. Here's how to create a calendar table covering a 100-year period in SQL:

<code class="language-sql">-- 开始日期：1901年1月1日
-- 结束日期：2099年12月31日
DECLARE @StartDate DATETIME = '19010101';
DECLARE @EndDate DATETIME = '20991231';

-- 创建日历表
CREATE TABLE Calendar (
    CalendarDate DATETIME NOT NULL
);

-- 将日期插入日历表
WHILE @StartDate <= @EndDate
BEGIN
    INSERT INTO Calendar (CalendarDate) VALUES (@StartDate);
    SET @StartDate = DATEADD(day, 1, @StartDate);
END;</code>

This script will create a calendar containing every day between January 1, 1901 and December 31, 2099. You can then use this table to extract date-related information from the data. For example, the following query will return the number of days between two dates:

<code class="language-sql">SELECT DATEDIFF(day, StartDate, EndDate)
FROM Calendar
WHERE StartDate >= '20230101' AND EndDate <= '20230331';</code>

The result of this query will be 90 because there are 90 days between January 1, 2023 and March 31, 2023.

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