Occasionally, it's necessary to convert character data (char, nchar, varchar, nvarchar) to a number. Before doing so, it is best to make sure that the value can be converted to a number.
IsNumeric would be the obvious choice, but has some problems because it allows for unexpected characters during the conversion. For example, the following strings will return true from the IsNumeric function.
Often times, we don't want to allow the dollar sign or scientific notation.
To make sure a value can be converted to an integer, you can append .0e0 to the end of the string before checking. If the original value had a decimal point, then adding another decimal point will cause the value to not be numeric. Similarly, adding e0 to a value that is already expressed in scientific notation will cause IsNumeric to return false.
Notice how the second column will only evaluate to true for the value that can be converted to an integer. Als notice how the 3rd column will only evaluate to true for the last 2 values.
You can create your own User Defined Function to check for integers, like so:
CODE
CREATE Function dbo.IsInteger(@Value VarChar(18)) Returns Bit As Begin
Return IsNull( (Select Case When CharIndex('.', @Value) > 0 Then Case When Convert(int, ParseName(@Value, 1)) <> 0 Then 0 Else 1 End Else 1 End Where IsNumeric(@Value + 'e0') = 1), 0)
End
To use this new function:
Select Convert(int, field) From Table Where dbo.IsInteger(field) = 1
If you want to allow fractional numbers, then you can add e0 to the isnumeric test.
Again, you can create a User Defined Function to test this.
CODE
Create Function IsNumber(@Value VarChar(18)) Returns Bit As Begin Return (Select IsNumeric(@Value + 'e0')) End
After creating the User Defined Functions, you can test it with the following code.
CODE
Declare @Temp Table(Data VarChar(18))
Insert Into @Temp Values('$12.09') Insert Into @Temp Values('1.4e3') Insert Into @Temp Values('2d4') Insert Into @Temp Values('3.7') Insert Into @Temp Values('412')
Select Data, IsNumeric(Data) As [IsNumeric], dbo.IsInteger(Data) As IsInteger, dbo.IsNumber(Data) As IsNumber From @Temp
Special thanks to SQLDenis for helping me work out the exceptions in the IsInteger function.
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