Question

I need to insert numbers with decimals into a SQL Server 2008 database. It seems like decimal() is the correct data type to use, however, I’m having trouble understanding it exactly.

I found this script (scroll down for decimal):

http://www.sqlteam.com/forums/topic.asp?TOPIC_ID=95322

Which allows me to test different decimal settings against numbers, and there’s some I don’t understand why they pass or fail. The way I understand it, when using decimal(precision, scale), precision is the number of digits to the left of the decimal and scale is the number of digits to the right of the decimal. Using this function, I don’t understand why some are passing and why some are failing.

SELECT dbo.udfIsValidDECIMAL('2511.1', 6, 3)    

I have 4 digits on the left and 1 on the right, yet this fails.

SELECT dbo.udfIsValidDECIMAL('10.123456789123456789', 18, 17)    
SELECT dbo.udfIsValidDECIMAL('10.123456789123456789', 18, 16)

The first one fails, the second one passes. There are 18 digits after the decimal point, so it seems like both should fail (or pass and SQL truncates the number).

Maybe I have a fundamental misunderstanding in how decimal() is supposed to work?

Answer 1

Precision is the number of digits that can be stored total.

So the number to the left of the decimal will be precision – scale.

For example, your first example will fail because you are only allowing for three places to the left of the decimal:

SELECT dbo.udfIsValidDECIMAL('2511.1',6,3)