SQL Server CAST vs CONVERT: A Comprehensive Guide for Devs

Greetings, Dev! As a developer, you must have come across the terms “CAST” and “CONVERT” in SQL Server. Both of these functions are used to convert data types in SQL Server. In this article, we will delve into the differences between these two functions so that you can choose the right one for your specific data type conversion needs.

What is SQL Server CAST?

Casting is the process of converting one data type to another data type. The CAST function in SQL Server is used to explicitly convert values from one data type to another. It has the following syntax:

The “expression” parameter in the CAST function can be a literal or a column name. The “data_type” parameter specifies the target data type to which the expression is to be converted.

Examples:

Let’s say you have a table named “employees” with a column “salary” defined as INT. You want to convert the “salary” column to DECIMAL(10,2). Here is how you can use the CAST function:

The above query will return a new column “new_salary” with values rounded to 2 decimal places.

What is SQL Server CONVERT?

The CONVERT function in SQL Server is also used to convert data types, but it provides more flexibility than the CAST function. It has the following syntax:

The “expression” parameter in the CONVERT function can be a literal or a column name. The “data_type” parameter specifies the target data type to which the expression is to be converted. The optional “style” parameter specifies the format of the output string, which is used only when converting to character data types like VARCHAR.

Examples:

Let’s say you have a table named “orders” with a column “order_date” defined as DATETIME. You want to convert the “order_date” column to CHAR(10) format. Here is how you can use the CONVERT function:

The above query will return a new column “order_date_char” with values in MM/DD/YYYY format.

CAST vs CONVERT: What’s the Difference?

Now that you know the basics of CAST and CONVERT functions, let’s explore their differences.

1. Flexibility:

The CONVERT function is more flexible than the CAST function because it allows you to specify a style parameter for character data types. The style parameter determines the format of the output string when converting to character data types. However, if you do not need to format the output string, you should use the CAST function because it is faster and simpler.

2. Precision:

The CONVERT function provides more precision than the CAST function for data types like FLOAT and DECIMAL. If you need more precision, you should use the CONVERT function.

3. Performance:

The CAST function is faster than the CONVERT function because it does not need to consider style parameters. If you do not need to format the output string, you should use the CAST function for better performance.

FAQs

Q. Can I use CAST to convert non-numeric data types?

A. No. The CAST function can only be used to convert numeric data types. If you want to convert non-numeric data types like VARCHAR to DATETIME, you should use the CONVERT function.

Q. Which function should I use when converting data types?

A. It depends on your specific needs. If you need to format the output string, you should use the CONVERT function with a style parameter. If you do not need to format the output string, you should use the CAST function for better performance. However, if you need more precision, you should use the CONVERT function.

Q. Are there any other data type conversion functions in SQL Server?

A. Yes. SQL Server provides many other data type conversion functions like TRY_CONVERT, TRY_CAST, PARSE, and TRY_PARSE. These functions are used for data type conversion with error handling or null-handling capabilities.

Q. Can I convert a data type to a user-defined data type?

A. Yes. If you have defined a user-defined data type, you can use the CAST or CONVERT function to convert a data type to your user-defined data type.

Q. Can I cast or convert a column with NULL values?

A. Yes. The CAST and CONVERT functions can handle NULL values by returning a NULL value if the expression or column being converted is NULL.

Conclusion

In this article, we have discussed the differences between SQL Server CAST and CONVERT functions. We have also covered their syntax, examples, and FAQs. The choice between CAST and CONVERT function depends on your specific data type conversion needs. Remember to use the CAST function for better performance and the CONVERT function for more flexibility and precision. We hope that this article has helped you in understanding these functions better.