Скачать или смотреть How to Convert char Data Type to Date in SQL Server

Learn how to correctly convert `char` data types to `date` formats in SQL Server, with practical examples and tips for best practices in database design.
---
This video is based on the question https://stackoverflow.com/q/64832686/ asked by the user 'Zahra' ( https://stackoverflow.com/u/11910283/ ) and on the answer https://stackoverflow.com/a/64832754/ provided by the user 'Thom A' ( https://stackoverflow.com/u/2029983/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to convert char data type to date in SQL Server?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Converting char Data Type to date in SQL Server

When working with databases, one common challenge developers face is data type conversion. Specifically, converting a char data type to a date format in SQL Server can be crucial for ensuring data integrity and facilitating accurate date-related queries. In this guide, we’ll address a specific scenario: converting a char(10) column containing date values in the format 2020/05/06 into an actual date data type.

The Problem

Imagine having a column named BeginDate in your SQL Server table, defined as char(10). Each record in this column is formatted as 2020/05/06. Storing date values as char can lead to various issues, especially when performing date calculations or filtering results based on date criteria.

Why is This a Problem?

Data Integrity: Storing dates as strings can introduce errors during data entry, leading to inconsistencies.

Performance: Date calculations on string types are less efficient than those performed on date types.

Query Complexity: Filtering or sorting operations can become more complicated when dealing with strings instead of dates.

The Solution

To convert a char type to a date in SQL Server, you can utilize the TRY_CONVERT function. This function attempts to convert a value to a specified data type and returns a NULL value if the conversion fails, which helps to prevent errors in your queries.

Step-by-Step Guide to Conversion

1. Replace the Separator

Since the dates are formatted with slashes ( / ), the first step is to remove these characters. By replacing them with an empty string, you convert the format to yyyyMMdd, which is recognized as a standard date format in SQL Server.

2. Use the TRY_CONVERT Function

Here's the SQL command to perform the conversion:

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

Breakdown of the Code:

TRY_CONVERT(date, ...): This part specifies that we want to convert the string into a date type.

REPLACE(BeginDate, '/', ''): This replaces the slashes with nothing, resulting in a continuous string of digits.

112: This is a style code that corresponds to the yyyyMMdd format.

3. Best Practices for Future Development

While the above method will effectively convert your char dates into the appropriate format, it’s important to consider the broader implications of your database design regarding date storage. Here are some recommendations:

Avoid Storing Dates as Strings: Use the appropriate date data types such as date, datetime, or datetime2 for storing date values. This ensures better data integrity and performance.

Data Validation: Implement checks on input data to ensure that only valid date formats are accepted, thus reducing conversion issues at the database level.

Revise Existing Data Structures: If you have columns storing dates as strings, consider converting them to date types as part of a data migration strategy.

Conclusion

Converting a char data type to a date in SQL Server doesn't have to be complicated. By using the TRY_CONVERT function and cleaning up the format beforehand, you can effortlessly achieve accurate date representations. However, it’s essential to rethink how dates are managed in your database to avoid similar issues in the future. Remember, proper database design can save you time and effort down the road.

Happy coding and happy database managing!