The TRY_CONVERT function in SQL Server is used to convert an expression from one data type to another. Unlike CONVERT, if TRY_CONVERT fails to convert the value, it returns NULL instead of throwing an error. This makes it useful for error handling during type conversion.
The syntax for TRY_CONVERT is:
TRY_CONVERT(data_type, expression [, style])
- data_type: The target data type you want to convert to (e.g., INT, VARCHAR, DATETIME, etc.).
- expression: The value you want to convert.
- style: An optional parameter that specifies the format for the conversion, which is applicable for certain data types (e.g., date formats).
Example of TRY_CONVERT with Different Data Types
Here’s an example that demonstrates how to use TRY_CONVERT with different data types along with error handling.
Suppose we have a table called DataSamples with a column SampleValue that contains various types of data (strings, numbers, dates).
Example Table Creation
CREATE TABLE DataSamples (
SampleValue VARCHAR(50)
);
INSERT INTO DataSamples (SampleValue) VALUES
('10'), -- Valid INT
('ABC'), -- Invalid INT
('2023-01-01'), -- Valid DATETIME
('NotADate'), -- Invalid DATETIME
('3.14'); -- Valid FLOAT
Using TRY_CONVERT to Handle Conversions
Here’s how you can use TRY_CONVERT to attempt conversions from SampleValue to INT, DATETIME, and FLOAT types while handling potential conversion errors:
SELECT
SampleValue,
TRY_CONVERT(INT, SampleValue) AS ConvertedToInt,
TRY_CONVERT(DATETIME, SampleValue) AS ConvertedToDateTime,
TRY_CONVERT(FLOAT, SampleValue) AS ConvertedToFloat
FROM
DataSamples;
Explanation of Results
1. For the row with SampleValue of '10', TRY_CONVERT(INT, '10') will return 10, and both other conversions will return NULL.
2. For the row with SampleValue of 'ABC', TRY_CONVERT(INT, 'ABC') will return NULL, and the other conversions will also return NULL.
3. For the row with SampleValue of '2023-01-01', the TRY_CONVERT(DATETIME, '2023-01-01') will return the corresponding datetime value, and both other conversions will return NULL.
4. For the row with SampleValue of 'NotADate', it will return NULL for the datetime conversion and the other conversions might also return NULL.
5. For the row with SampleValue of '3.14', it will successfully convert to FLOAT, while the other conversions will return NULL.
Summary
TRY_CONVERT is a powerful function for safely converting data types in SQL Server. It allows you to handle potential conversion errors gracefully by returning NULL when a conversion fails, rather than throwing an error which could disrupt further query processing. This makes it particularly useful in data cleaning and transformation tasks where you expect some invalid formats.