Len function on Float in SQLServer gives wrong length

Question

I am using the below query in SQL Server.

declare @dt float
set @dt = 1079938.05
select @dt AS Val,Convert(nvarchar(20),@dt) AS NVal, len(@dt) AS Len
         


        

Answer 1

A float in sql server can be 4 or 8 byte. Find details.

LEN() is a function to measure the lenght of a string. So you want to measure the length of the string representation of the value, not the value itself.

The shown display value 1.07994e+006 is scientific notation and has 12 characters. Nothing wrong here.

Your call Convert(nvarchar(20),@dt) calls the CONVERT()-function with the defaul for FLOAT and REAL(Details and other formats here), which is scientific for numbers larger than 6 digits. The same happens implicitly when you call 'len(@dt)'. As the input of LEN() must be a string, the value is converted and then passed to the function.

What you can do:

• You might think about a conversion to DECIMAL...

• Another choice was first to use STR()-function together with RTRIM().

• One more choice was FORMAT()-function (SQL Server 2012+) .

Anyway you have to consider, that the text you see is not the real value.

Answer 2

LEN() works on [N]VARCHAR(), thus you're running into an implicit conversion from FLOAT to VARCHAR

see this: https://social.msdn.microsoft.com/Forums/sqlserver/en-US/a4ea2bc1-6f2f-4992-8132-f824fe4ffce0/length-of-float-values-in-ms-sql-server-gives-wrong-result?forum=transactsql

That means that LEN converts the value to VARCHAR before it actually calculates its length. That's because the length you get coincides with the length of your NVarChar value 1.07994e+006.

Answer 3

First of all: Don't use approximate data types when not forced to. A FLOAT is just an approximation, e.g. a simple value like 0.123 may be stored as 0.1230000000001 for instance. Use a precise type such as DECIMAL instead.

When converting a number to a string, you should usually specify a format as in format(@dt, '#,###,##0.00'). You don't do so, so it's up to the system what format to use. It uses a scientific notation 1.07994e+006 translating to 1.079940 x 10^6, which is approximately your number.