How to Do Type Casting in SQL Server

Type casting in SQL Server is a process of converting one data type to another. This is commonly required when performing operations that involve multiple data types. SQL Server provides two main functions for type casting: CAST() and CONVERT().

What is Type Casting?

Type casting refers to the process of converting a value from one data type to another. In SQL Server, this might be necessary when you're performing arithmetic operations, joining tables with different data types, or when you want to display a result in a specific format.

Methods for Type Casting in SQL Server

1. CAST()

The CAST() function is used to explicitly convert an expression from one data type to another. It has the following syntax:

CAST(expression AS target_data_type)

For example, to convert a VARCHAR value to an INT:

SELECT CAST('123' AS INT);

This will return 123 as an integer.

2. CONVERT()

The CONVERT() function works similarly to CAST(), but it provides additional formatting options, especially for date and time conversions. The syntax is:

CONVERT(target_data_type, expression, style)

For instance, to convert a DATETIME value to a VARCHAR with a specific date format:

SELECT CONVERT(VARCHAR, GETDATE(), 103);

This will return the current date in the format dd/mm/yyyy.

Example: Using CAST() and CONVERT() Together

In some scenarios, you may need to combine both functions. For example, you might cast a value to a specific data type and then convert it into a formatted string.

SELECT CONVERT(VARCHAR, CAST(GETDATE() AS DATE), 103);

This will first cast the current date and time to a DATE and then convert it to a VARCHAR with the dd/mm/yyyy format.

Why Use Type Casting?

Type casting is essential in SQL Server when you're dealing with expressions that involve multiple data types. Without casting, SQL Server may throw errors or produce unexpected results. It's particularly useful when working with:

• Comparing different data types in queries
• Performing calculations across different data types
• Displaying values in a specific format

Conclusion

Type casting in SQL Server helps you manage and manipulate data types effectively. By using the CAST() and CONVERT() functions, you can ensure that your data is in the right format for calculations, comparisons, and presentation.