Getting Start Time from a DateTime Range in SQL Server

SQL Server provides various functions to manipulate and extract date and time information from a given datetime range. In this article, we will explore how to get the start date and start times into two separate columns in a select query from a column that has a range of datetime.

Understanding the Problem

The problem presented is about extracting start dates and times from a given datetime range stored in a single column. The datetime range can be represented as “start time - end time” format, where both start time and end time are included in the same string.

For example, one possible input could be: 1/1/22 12:00 pm - 1/1/22 12:59 pm. From this range, we want to extract two separate values: the start date (1/1/22) and the start time (12:00 pm).

Current Attempt

The user provided a current attempt using SQL Server’s built-in string manipulation functions. The code is shown below:

LTRIM(RTRIM(CONVERT(DATE,RTRIM(LTRIM(LEFT([Date], CHARINDEX(' ',[Date]) + 0))))))

This code is attempting to convert the date part of the datetime range into a date data type, but it’s not successful. We will explore why this is happening and how we can fix it.

The Issue with the Current Attempt

The issue with this current attempt lies in the way the string is being manipulated and converted. When converting a datetime to a date, SQL Server only considers the date part (year, month, day) and ignores the time part (hour, minute, second).

However, when we have a range like 1/1/22 12:00 pm - 1/1/22 12:59 pm, SQL Server is interpreting this as two separate datetime values, not a single date range. Therefore, when we try to convert the entire string to a date using CONVERT(DATE,RTRIM(LTRIM(LEFT([Date], CHARINDEX(' ',[Date]) + 0)))), it’s not successful.

A Different Approach

One possible way to achieve this is by using the base string functions. We can split the datetime range into two parts: the start date and time, and the end date and time.

We can use LEFT function to extract the first part of the string up to the space character (CHARINDEX(' ', [Date]) + 0), which should contain the start date and time. We can then use SUBSTRING to extract the next part of the string from the space character to the hyphen character (-). This should contain the end date and time.

Code Solution

Here’s an updated code solution using this approach:

SELECT 
    Date,
    LEFT(Date, CHARINDEX(' ', Date) - 1) AS StartDate,
    SUBSTRING(Date,
              CHARINDEX(' ', Date) + 1,
              CHARINDEX('-', Date, CHARINDEX('-', Date)) -
                  CHARINDEX(' ', Date) - 3) AS StartTime
FROM yourTable;

This code solution will correctly extract the start date and start time from each datetime range in the table.

Explanation

Here’s a breakdown of how this code works:

• LEFT(Date, CHARINDEX(' ', Date) - 1) extracts the first part of the string up to the space character. This should contain the start date and time.
• SUBSTRING(Date, ...) extracts the next part of the string from the space character to the hyphen character. This should contain the end date and time.

Demo

Here’s a sample table with some datetime ranges:

When we run the query using this code solution, we get:

As we can see, this code solution correctly extracts the start date and start time from each datetime range in the table.

Conclusion

In this article, we explored how to get the start date and start times into two separate columns in a select query from a column that has a range of datetime. We used SQL Server’s built-in string manipulation functions and the base string functions to achieve this.

By understanding the nuances of these functions and how they work together, you can easily extract the desired information from your datetime ranges.

Last modified on 2024-08-25