Converting decimal and numeric Data
For the decimal and numeric data types, Microsoft® SQL Server™ considers each specific combination of precision and scale as a different data type. For example, decimal(5,5) and decimal(5,0) are considered different data types.
In Transact-SQL statements, a constant with a decimal point is automatically converted into a numeric data value, using the minimum precision and scale necessary. For example, the constant 12.345 is converted into a numeric value with a precision of 5 and a scale of 3.
Converting from decimal or numeric to float or real can result in some loss of precision. Converting from int, smallint, tinyint, float, real, money, or smallmoney to either decimal or numeric can result in overflow.
By default, SQL Server uses rounding when converting a number to a decimal or numeric value with a lower precision and scale. However, if the SET ARITHABORT option is ON, SQL Server raises an error when overflow occurs. Loss of only precision and scale is not sufficient to raise an error.