How CONVERT works in SQL? Best CONVERT examples

How CONVERT works in SQL? Best CONVERT examples

When working with SQL, I often find myself needing to transform data from one type to another. This is where the CONVERT function comes into play. It’s an essential tool for handling type conversions in SQL Server. Whether you’re dealing with strings, dates, or numbers, CONVERT can help ensure your data is in the right format.

What is the CONVERT Function in SQL?

The CONVERT function in SQL Server allows you to explicitly change the data type of an expression. It is particularly useful when working with different data types that need to be harmonized, such as converting dates to strings or numbers to text.

Here’s the basic syntax of the CONVERT function:

CONVERT(target_data_type, expression, style)
  • target_data_type – The desired data type you want to convert the expression to.
  • expression – The value you want to convert.
  • style (optional) – A numeric code used for defining how the conversion should happen, mainly useful when dealing with dates or numbers.

Common Use Cases for CONVERT

To fully understand CONVERT, let’s look at some practical use cases.

1. Converting Dates to Different Formats

One of the most common uses of CONVERT is formatting datetime values. SQL Server allows using a style code to format dates in specific ways.

SELECT CONVERT(VARCHAR, GETDATE(), 101) AS US_Format;
SELECT CONVERT(VARCHAR, GETDATE(), 103) AS UK_Format;
SELECT CONVERT(VARCHAR, GETDATE(), 120) AS ISO_Format;

Here’s what the output might look like:

Format Example Output
US Format (101) 06/14/2024
UK Format (103) 14/06/2024
ISO Format (120) 2024-06-14 12:34:56

2. Converting Numbers to Strings

Sometimes, I need to convert numeric values into string format, especially for reporting or concatenation.

SELECT CONVERT(VARCHAR, 12345) AS StringValue;

Output:

StringValue
---------
12345

3. Converting Strings to Numbers

Trying to perform calculations on values stored as strings? You’ll need CONVERT to change them into a numeric type first.

SELECT CONVERT(INT, '100') + 50 AS Result;

Output:

Result
------
150

Key Differences Between CONVERT and CAST

SQL Server offers another function called CAST, which also handles type conversion. While both functions are similar, there are some important differences:

  • CONVERT provides more control over date formatting using the style argument.
  • CAST follows ANSI SQL standards, making it more portable across different databases.

For basic conversions, both work well, but when formatting precision is required, I prefer CONVERT.

CONVERT Function Best Practices

Here are some best practices to keep in mind when using CONVERT:

  1. Always verify that the conversion is valid to avoid runtime errors.
  2. Use the style parameter wisely when converting dates.
  3. Avoid unnecessary conversions for performance optimization.
  4. Prefer CAST when working with cross-database scenarios.

Final Thoughts

Understanding how CONVERT works in SQL can save a lot of headaches, especially when dealing with different data types in queries. Whether you need to format dates, change variable types, or manipulate strings, this function is an invaluable tool in SQL Server.

 

Other interesting article:

How CAST works in SQL? Best CAST examples