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

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Larry Thompson

To convert one data type to another in SQL Server, you can use the built-in conversion functions provided by the SQL Server. These functions allow you to transform data from one type to another, ensuring compatibility and consistency within your database.

Implicit Data Type Conversion

In some cases, SQL Server can automatically convert data from one type to another without explicitly specifying a conversion function. This is known as implicit data type conversion.

For example, if you try to compare an integer value with a decimal value in a WHERE clause, SQL Server will automatically convert the integer value to a decimal before performing the comparison.

Explicit Data Type Conversion

Sometimes, implicit data type conversion may not work as expected or you may need to explicitly convert data between different types. In such cases, you can use the explicit conversion functions provided by SQL Server.

The most commonly used explicit conversion functions are:

  • CAST: This function allows you to convert one data type to another by specifying the Target data type.
  • CONVERT: This function also allows you to convert one data type to another. It provides more flexibility in terms of formatting options for certain data types like dates and times.

Let’s look at some examples:

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

-- Using CONVERT
SELECT CONVERT(INT, '456') AS ConvertedValue;

-- Converting date format using CONVERT
SELECT CONVERT(VARCHAR(10), GETDATE(), 101) AS FormattedDate;

Numeric Conversion Functions

In addition to CAST and CONVERT, SQL Server provides specific conversion functions for handling numeric data types:

  • ROUND: This function rounds a numeric value to a specified length or precision.
  • FLOOR: This function returns the largest integer less than or equal to the specified numeric value.
  • CEILING: This function returns the smallest integer greater than or equal to the specified numeric value.

Here’s an example:

SELECT ROUND(12.3456, 2) AS RoundedValue;
SELECT FLOOR(12.3456) AS FlooredValue;
SELECT CEILING(12.3456) AS CeiledValue;

Conclusion

In SQL Server, converting data from one type to another is essential for ensuring data integrity and compatibility. Whether you need to perform an explicit conversion using CAST or CONVERT, or utilize specific numeric conversion functions like ROUND, FLOOR, and CEILING – SQL Server provides a range of options to handle data type conversions effectively.

By understanding how to convert data types in SQL Server and utilizing the appropriate conversion functions, you can manipulate and transform data with confidence, making your database operations more efficient and accurate.

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