The TRY_CAST function is used in SQL to attempt to convert a value from one data type to another without causing an error if the conversion fails. Instead of throwing an error when the conversion is not possible, TRY_CAST returns NULL.
Here's the general syntax for TRY_CAST:
TRY_CAST(expression AS target_data_type)
Parameters:
- expression: The value that you want to convert.
- target_data_type: The data type you want to convert the expression to (e.g., int, varchar, datetime, etc.).
Example Usage:
Suppose you have a table with a column that stores numbers as strings, and you want to convert these strings to integers safely. Here’s how you could do it with TRY_CAST:
SELECT
original_value,
TRY_CAST(original_value AS INT) AS converted_value
FROM
your_table
Explanation:
- In this example, original_value is a column containing the string representations of numbers.
- The result of TRY_CAST(original_value AS INT) will be the integer value if the conversion is successful. If original_value cannot be converted to an integer (for example, it contains non-numeric characters), the result will be NULL.
Considerations:
- TRY_CAST is especially useful in situations where data integrity cannot be guaranteed, such as when importing data from external sources.
- Always check for NULL values in the result set to handle cases of failed conversions appropriately.
Example with Error Handling:
You can also use TRY_CAST in a WHERE clause to filter out values that cannot be converted:
SELECT
original_value
FROM
your_table
WHERE
TRY_CAST(original_value AS INT) IS NOT NULL
This query will return only those records where the original_value can be successfully converted to an integer.