How to Convert Varchar Date and Time to DataTime in T-SQL

Learn how to effectively convert varchar date and time columns into a single datetime format using T-SQL. Explore methods, best practices, and tips for SQL Server.
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Converting Varchar Date and Time to DataTime in T-SQL

Handling date and time data types can often be tricky, especially when interfacing with varchar fields in SQL Server. This guide addresses a common challenge: converting two separate varchar columns—MyDate and MyTime—into a single datetime column using T-SQL. If you’ve been wrestling with this issue, you’re in the right place!

The Problem

You have a table called MyTable with two columns defined as follows:

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For example, let’s say the columns contain the following values:

MyDate = '20220306' (March 6, 2022)

MyTime = '171638' (5:16:38 PM)

Your goal is to combine both columns into a single datetime value. While you can easily convert MyDate to a date type, the transformation for MyTime is where complications arise.

Many SQL users struggle to find the correct method for the time conversion, often resulting in inefficient queries or errors. Let’s dive into how you can tackle this problem effectively.

The Solution

The most effective method we can use involves two main conversions: first, converting the date and then constructing the time from the varchar representation. Here’s how to do it:

Step 1: Convert the Date

The date conversion can be done using the CAST function to convert MyDate as follows:

[[See Video to Reveal this Text or Code Snippet]]

This SQL statement successfully converts the varchar date into a proper date type, but it’s only half the solution.

Step 2: Format the Time

To convert the MyTime varchar to a time value, we need to manipulate the string. The procedure below formats the MyTime field into hours, minutes, and seconds:

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By breaking down the MyTime string:

LEFT(MyTime, 2) gets the first two characters (hours).

SUBSTRING(MyTime, 3, 2) retrieves the next two characters (minutes).

RIGHT(MyTime, 2) captures the last two characters (seconds).

Step 3: Combine Both Components into a Datetime

Finally, combine the converted date and the formatted time into a single datetime value:

[[See Video to Reveal this Text or Code Snippet]]

Optional: Change Data Types for Future Use

While the above method works well, consider changing the data types of these columns in your database for more efficient handling. By storing these fields as DATE and TIME types from the start, you can avoid cumbersome conversions in the future.

Final Thoughts

Converting varchar date and time to a single datetime field in T-SQL is straightforward with the right approach. By following the steps outlined above, you can efficiently obtain the desired result while maintaining code clarity.

If you have any questions or would like to share your experiences with T-SQL date and time conversions, feel free to leave a comment below!