How to Use SQL Convert

If you need to change the data type of a value stored in a SQL Server database, you can use the SQL CONVERT function. This function allows you to convert data from one type to another. In this tutorial, you will learn how to use the SQL CONVERT function.

Syntax

Here is the syntax for the SQL CONVERT function:

CONVERT(data_type, expression, [style])

The data_type parameter specifies the target data type. The expression parameter specifies the value to be converted. The style parameter is optional and specifies the format of the output.

Examples

Example 1: Convert a String to an Integer

Suppose you have a table called employees that contains a column called employee_id. The employee_id column is currently stored as a string, but you want to convert it to an integer. Here’s how you can do it:

SELECT employee_id, CONVERT(INT, employee_id) AS employee_id_int
FROM employees

This query will return a result set with two columns: employee_id (the original string value) and employee_id_int (the converted integer value).

Example 2: Convert a Date to a String

Suppose you have a table called orders that contains a column called order_date. The order_date column is currently stored as a date, but you want to convert it to a string in the format of “YYYY-MM-DD”. Here’s how you can do it:

SELECT order_id, CONVERT(VARCHAR(10), order_date, 120) AS order_date_str
FROM orders

This query will return a result set with two columns: order_id (the original value) and order_date_str (the converted string value).

Style Parameter

The style parameter is optional and specifies the format of the output. The format codes are specific to each data type. For example:

• For dates:
  • 101: mm/dd/yyyy
  • 102: yyyy.mm.dd
  • 120: yyyy-mm-dd hh:mi:ss (24 hour clock)
• For floats and decimals:
  • 0: (default) no commas or decimal points
  • 1: commas for thousands, no decimal point
  • 2: commas for thousands and a decimal point

Here’s an example of using the style parameter to convert a date to a string in a specific format:

SELECT order_id, CONVERT(VARCHAR(10), order_date, 101) AS order_date_str
FROM orders

This query will convert the order_date to a string in the format of “mm/dd/yyyy”.

Troubleshooting Tips

• Make sure the data_type parameter is a valid SQL Server data type.
• If you get an error message, double-check the syntax of your query and make sure all parameters are spelled correctly.
• If you’re converting a string to an integer, make sure the string only contains numerical characters. Otherwise, you may get an error message.

Conclusion

In this tutorial, you learned how to use the SQL CONVERT function to convert data from one type to another. You also learned how to use the style parameter to format the output. With this knowledge, you can now manipulate your SQL Server data in new and useful ways.