How do I count decimal places in SQL?

Question

I have a column X which is full of floats with decimals places ranging from 0 (no decimals) to 6 (maximum). I can count on the fact that there are no floats with greater than 6 decimal places. Given that, how do I make a new column such that it tells me how many digits come after the decimal?

I have seen some threads suggesting that I use CAST to convert the float to a string, then parse the string to count the length of the string that comes after the decimal. Is this the best way to go?

Answer 1

You can use something like this:

declare @v sql_variant

set @v=0.1242311

select SQL_VARIANT_PROPERTY(@v, 'Scale') as Scale

This will return 7.

---

I tried to make the above query work with a float column but couldn't get it working as expected. It only works with a sql_variant column as you can see here: http://sqlfiddle.com/#!6/5c62c/2

So, I proceeded to find another way and building upon this answer, I got this:

SELECT value,
LEN(
    CAST(
         CAST(
              REVERSE(
                      CONVERT(VARCHAR(50), value, 128)
                     ) AS float
             ) AS bigint
        )
   ) as Decimals
FROM Numbers

Here's a SQL Fiddle to test this out: http://sqlfiddle.com/#!6/23d4f/29

---

To account for that little quirk, here's a modified version that will handle the case when the float value has no decimal part:

SELECT value,
       Decimals = CASE Charindex('.', value)
                    WHEN 0 THEN 0
                    ELSE
           Len (
            Cast(
             Cast(
              Reverse(CONVERT(VARCHAR(50), value, 128)) AS FLOAT
                 ) AS BIGINT
                )
               )
                    END
FROM   numbers

Here's the accompanying SQL Fiddle: http://sqlfiddle.com/#!6/10d54/11

Answer 2

This thread is also using CAST, but I found the answer interesting:

http://www.sqlservercentral.com/Forums/Topic314390-8-1.aspx

DECLARE @Places INT
 SELECT TOP 1000000 @Places = FLOOR(LOG10(REVERSE(ABS(SomeNumber)+1)))+1
   FROM dbo.BigTest

and in ORACLE:

SELECT FLOOR(LOG(10,REVERSE(CAST(ABS(.56544)+1 as varchar(50))))) + 1 from DUAL