How Do I Convert One Data Type to Another in SQL?


Angela Bailey

In SQL, converting one data type to another is a common task that you may come across while working with databases. This process, known as data type conversion, allows you to change the format of data stored in a column or variable.

Implicit Data Type Conversion

SQL provides implicit data type conversion, which automatically converts one data type to another without the need for explicit instructions. This occurs when you perform operations or comparisons between different data types.

For example, if you try to add an integer value to a decimal column, SQL will automatically convert the integer value to a decimal before performing the addition. Similarly, if you compare a string value with an integer column, SQL will convert the string to an integer for comparison.

Explicit Data Type Conversion

Sometimes, you may need to explicitly convert data from one type to another. This can be useful when you want to ensure compatibility between different types or when performing specific calculations or transformations.

To explicitly convert one data type to another in SQL, you can use the CAST or CONVERT functions. Both functions allow you to specify the Target data type and convert the input value accordingly.

The syntax for using these functions is as follows:

  • CAST(expression AS datatype)
  • CONVERT(datatype, expression)

The CAST function is ANSI standard and widely supported across different database systems. The CONVERT function is specific to Microsoft SQL Server but offers additional flexibility in terms of formatting options.


To illustrate how explicit data type conversion works in SQL, let’s consider a few examples:

Example 1:


This query converts the string value ‘123’ to an integer using the CAST function. The result will be the number 123.

Example 2:

SELECT CONVERT(DATE, '2022-01-01');

In this example, the CONVERT function is used to convert the string ‘2022-01-01’ to a date data type. The result will be a date value representing January 1, 2022.

Handling Conversion Errors

When converting data types in SQL, it’s important to consider potential errors that may occur. For example, if you attempt to convert a non-numeric string to an integer, an error will be thrown.

To handle conversion errors and prevent query failures, you can use error handling mechanisms such as TRY-CATCH blocks. These allow you to catch and handle exceptions that occur during data type conversion.

In Conclusion

Data type conversion is a common task in SQL when working with databases. Whether through implicit or explicit conversion, understanding how to convert one data type to another is crucial for ensuring data compatibility and performing calculations or transformations accurately.

Remember, implicit conversion happens automatically during operations or comparisons between different types, while explicit conversion requires the use of functions like CAST or CONVERT. Handle potential errors with appropriate error handling mechanisms like TRY-CATCH blocks.

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