What Is Explicit Data Type Conversion in SQL?


Heather Bennett

What Is Explicit Data Type Conversion in SQL?

Data type conversion is an essential aspect of working with databases. It allows us to convert data from one type to another, ensuring compatibility and consistency in our SQL queries.

There are two types of data type conversion: implicit and explicit. In this article, we’ll focus on explicit data type conversion in SQL and explore its significance.

Understanding Explicit Data Type Conversion

Explicit data type conversion, also known as type casting, involves manually converting a value from one data type to another. It is explicitly specified by the programmer or database administrator within the SQL query.

Explicit data type conversion comes into play when the database engine cannot automatically convert a value from one data type to another due to possible loss of information or incompatible formats.

Why Use Explicit Data Type Conversion?

In SQL, explicit data type conversion serves several purposes:

  • Data Integrity: By explicitly converting data types, we ensure that the values stored in the database match their intended meaning and avoid potential errors due to incompatible types.
  • Data Manipulation: Explicit conversions enable us to perform mathematical operations, comparisons, and other manipulations on different data types.
  • Data Presentation: Converting values into specific data types allows us to present them in a desired format for better readability or integration with other systems.

Syntax of Explicit Data Type Conversion

In SQL, explicit data type conversion is typically done using built-in functions or operators that facilitate the transformation process. The general syntax for explicit conversion is as follows:

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

The CAST and CONVERT functions take an expression (the value to be converted) and a Target data type as parameters. The database engine then attempts to convert the value to the specified data type.

Note: The specific syntax and available data types for explicit conversion may vary depending on the database management system (DBMS) you are using. It’s crucial to consult the documentation or reference materials for your specific DBMS.

Examples of Explicit Data Type Conversion

To illustrate explicit data type conversion, let’s consider a few examples:

Example 1: Converting a String to an Integer

We have a table named employees, which contains a column named age of integer data type. However, the values in this column are stored as strings. To perform numeric calculations on the age values, we need to convert them from strings to integers explicitly.

FROM employees;

In this example, we use the CAST function to convert the age column from string to integer. The resulting query will provide accurate numeric results for further calculations or comparisons.

Example 2: Converting a Date/Time Value to a Specific Format

Sometimes we may need to present date/time values in a particular format that is not the default representation used by our DBMS. In such cases, explicit conversion helps us achieve the desired presentation.

SELECT name, CONVERT(VARCHAR(10), hire_date, 105) AS formatted_hire_date
FROM employees;

In this example, we use the CONVERT function to convert the hire_date column to a specific format. The 105 parameter specifies the desired format, which represents the date as DD-MM-YYYY.


Explicit data type conversion in SQL plays a vital role in ensuring data integrity, enabling data manipulation, and facilitating data presentation. By explicitly converting values from one data type to another, we can maintain consistency and compatibility within our SQL queries. Understanding the syntax and proper usage of explicit data type conversion functions is crucial for working effectively with databases.

To summarize:

  • Explicit data type conversion, also known as type casting, involves manually converting a value from one data type to another in SQL.
  • Explicit conversions are necessary when automatic conversions are not possible due to incompatible types or loss of information.
  • The syntax for explicit conversion usually involves using functions like CAST or CONVERT, followed by the Target data type and the expression to be converted.
  • We use explicit conversions for maintaining data integrity, performing manipulations on different types, and presenting data in specific formats.

By mastering explicit data type conversion techniques, you can enhance your SQL skills and ensure smoother interactions with databases.

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