The ISNUMERIC function in SQL Server is a built-in function used to determine whether an expression can be evaluated as a numeric value. It's particularly useful in data validation, ensuring that data entered into a database column conforms to the expected numeric format. This function is essential for preventing errors and maintaining data integrity. For example, if you're expecting a price column to only contain numbers, you can use ISNUMERIC to check if the input is a valid number before storing it. It's important to note that ISNUMERIC considers various numeric formats, including integers, decimals, and scientific notation. However, it also considers strings that can be converted to numbers, which might not be ideal in all cases. For instance, it will return TRUE for strings like '+123' or '12.34'. Therefore, it's often combined with other checks or validation rules to ensure the data meets specific requirements. A more robust approach might involve using TRY_CONVERT to attempt conversion to a numeric type and checking for errors.
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