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


Scott Campbell

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

When working with databases, it’s common to encounter situations where you need to convert data from one datatype to another. SQL provides several functions and techniques that allow you to perform these conversions seamlessly. In this tutorial, we will explore some of the most commonly used methods for converting datatypes in SQL.

1. Using CAST()

The CAST() function is a powerful tool for converting one datatype to another in SQL. It allows you to explicitly define the Target datatype and convert the source value accordingly.

To use the CAST() function, you need to specify the value you want to convert and the Target datatype inside the function. Here’s an example:

SELECT CAST('123' AS INT) AS ConvertedValue;

This query will convert the string ‘123’ into an integer using the CAST() function. The result will be a new column named ‘ConvertedValue’ with the converted integer value.

2. Using CONVERT()

The CONVERT() function is another popular method for converting datatypes in SQL. It works similar to CAST(), but provides more flexibility when dealing with specific data formats.

To use CONVERT(), you need to specify both the source value and its original datatype, followed by the Target datatype. Here’s an example:

SELECT CONVERT(VARCHAR(10), 123) AS ConvertedValue;

This query converts the integer value 123 into a varchar datatype with a length of 10 using the CONVERT() function. The result will be a new column named ‘ConvertedValue’ with the converted value.

3. Using Implicit Conversion

In some cases, SQL can automatically perform datatype conversion without the need for explicit functions like CAST() or CONVERT(). This is known as implicit conversion.

Implicit conversion occurs when you use an operator or function that expects a specific datatype, but you provide a different datatype. SQL will automatically convert the value to the expected datatype if it’s compatible.

For example, if you try to add an integer and a decimal value together, SQL will automatically convert the integer into a decimal before performing the addition.

SELECT 10 + 5.5 AS Result;

This query adds the integer value 10 and the decimal value 5.5 together. SQL will implicitly convert the integer into a decimal and return the result in the ‘Result’ column.

4. Using CASE Statement

The CASE statement in SQL can also be used for conditional datatype conversions. It allows you to evaluate conditions and perform different actions based on those conditions, including datatype conversions.

To use CASE for datatype conversion, you need to define multiple condition-value pairs and specify the Target datatypes for each pair. Here’s an example:

        WHEN Age >= 18 THEN 'Adult'
        ELSE 'Minor'
    END AS AgeGroup
FROM Users;

This query uses the CASE statement to evaluate whether a user’s age is greater than or equal to 18. If true, it returns ‘Adult’; otherwise, it returns ‘Minor’. The result will be a new column named ‘AgeGroup’ with the converted values.


In conclusion, converting datatypes in SQL is essential for handling various data manipulation tasks. Whether you need to convert strings to numbers or change one datatype to another, SQL provides several methods to accomplish these conversions. By using functions like CAST() and CONVERT(), leveraging implicit conversion, or utilizing the CASE statement, you can easily perform datatype conversions and ensure your data is properly formatted for your needs.

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