## SQL Server ISNUMERIC() Function – A Detailed Look at Numeric Types and Converting Strings to Numbers

When working with data in SQL Server, it is often necessary to determine whether a value is numeric or not. One common way of doing this is by using the ISNUMERIC() function.

This function is useful for validating input data, and it allows us to handle errors before they occur. In this article, we’ll take a deep dive into the ISNUMERIC() function and how it works.

## 1. ISNUMERIC() Function

The ISNUMERIC() function returns 1 if the input expression can be converted to any numeric type; otherwise, it returns 0. This function can be used to check whether a string is a valid numeric value or not.

For example,

```
SELECT ISNUMERIC('123') -- Returns 1
SELECT ISNUMERIC('abc') -- Returns 0
```

As you can see, the query returns 1 for the string ‘123’ because it is a numeric value, and 0 for the string ‘abc’ because it is not a numeric value. What is Considered a Valid Numeric Type?

### 1.1. Valid Numeric Types

The SQL Server numeric data types include exact numbers, fixed precision, approximate, and monetary values. The exact numbers include INT, SMALLINT, TINYINT, BIGINT, NUMERIC(p,s), and DECIMAL(p,s) data types.

The fixed precision numbers include FLOAT(n) and REAL data types. The approximate numbers include REAL, FLOAT(n), and FLOAT data types.

The monetary values include MONEY and SMALLMONEY data types.

## 2. Limitations of ISNUMERIC() Function

The ISNUMERIC() function has a few limitations. First, it returns 1 for values that may cause overflow when used in mathematical calculations.

Second, it does not work for some data types such as DATE, TIME, and DATETIMEOFFSET. To handle these limitations, you can use the TRY_CAST(), TRY_PARSE(), or TRY_CONVERT() function.

For example,

```
SELECT TRY_CAST('abc' AS INT) -- Returns NULL
SELECT TRY_PARSE('abc' AS INT) -- Returns NULL
SELECT TRY_CONVERT(INT, 'abc') -- Returns NULL
```

These functions return NULL if the conversion fails, and they do not cause an error.

## 3. Examples of ISNUMERIC() Function

### 3.1. Checking if a String Can Be Converted to a Number

Suppose we have a string value ‘$10’ that we want to convert to a number.

We can use the ISNUMERIC() function to check if it is a valid numeric value or not. For example,

`SELECT ISNUMERIC('$10') -- Returns 0`

The query returns 0 because ‘$10’ is not a valid numeric value.

### 3.2. Checking if a String is a Number in Scientific Notation

Scientific notation is a way of representing very large or very small numbers using exponential notation. For example, the number -2.23E-308 represents a very small number.

We can use the ISNUMERIC() function to check if a string is a number in scientific notation. For example,

`SELECT ISNUMERIC('-2.23E-308') -- Returns 1`

The query returns 1 because ‘-2.23E-308’ is a valid numeric value in scientific notation.

### 3.3. Checking if a String is Not a Number

Suppose we have a string value ‘+ABC’ that we want to check if it is a valid numeric value or not. We can use the ISNUMERIC() function to check this.

For example,

`SELECT ISNUMERIC('+ABC') -- Returns 0`

The query returns 0 because ‘+ABC’ is not a valid numeric value.

## 4. Conclusion

In conclusion, the ISNUMERIC() function in SQL Server is a useful tool for validating input data. It enables us to check whether a value is numeric or not.

The function has some limitations, but we can use other functions like TRY_CAST(), TRY_PARSE(), and TRY_CONVERT() to overcome these limitations. By harnessing the power of the ISNUMERIC() function, we can ensure that our SQL queries work as expected and avoid errors caused by invalid input data.

The ISNUMERIC() function in SQL Server is essential for validating input data to determine if a value is numeric or not. It works by returning 1 if the expression can be converted to any numeric type and 0 if it cannot.

The function is limited in some respects, such as not working with all data types. Still, we can use other functions like TRY_CAST(), TRY_PARSE(), and TRY_CONVERT() to overcome these limitations.

By harnessing the power of the ISNUMERIC() function, we can ensure that our SQL queries work as expected and avoid errors caused by invalid input data.