decimal and numeric (TransactSQL)
Updated: December 14, 2016
Numeric data types that have fixed precision and scale. Decimal and numeric are synonyms and can be used interchangeably.
decimal[ (p[ ,s] )] and numeric[ (p[ ,s] )]
Fixed precision and scale numbers. When maximum precision is used, valid values are from  10^38 +1 through 10^38  1. The ISO synonyms for decimal are dec and dec(p, s). numeric is functionally equivalent to decimal.
p (precision)
The maximum total number of decimal digits that will be stored, both to the left and to the right of the decimal point. The precision must be a value from 1 through the maximum precision of 38. The default precision is 18.



s (scale)
The number of decimal digits that will be stored to the right of the decimal point. This number is subtracted from p to determine the maximum number of digits to the left of the decimal point. The maximum number of decimal digits that can be stored to the right of the decimal point. Scale must be a value from 0 through p. Scale can be specified only if precision is specified. The default scale is 0; therefore, 0 <= s <= p. Maximum storage sizes vary, based on the precision.
Precision  Storage bytes 

1  9  5 
1019  9 
2028  13 
2938  17 



For the decimal and numeric data types, 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 TransactSQL 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 cause some loss of precision. Converting from int, smallint, tinyint, float, real, money, or smallmoney to either decimal or numeric can cause 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.
When converting float or real values to decimal or numeric, the decimal value will never have more than 17 decimals. Any float value < 5E18 will always convert as 0.
The following example creates a table using the decimal and numeric data types. Values are inserted into each column and the results are returned by using a SELECT statement.
CREATE TABLE dbo.MyTable ( MyDecimalColumn decimal(5,2) ,MyNumericColumn numeric(10,5) ); GO INSERT INTO dbo.MyTable VALUES (123, 12345.12); GO SELECT MyDecimalColumn, MyNumericColumn FROM dbo.MyTable;
Here is the result set.
MyDecimalColumn MyNumericColumn   123.00 12345.12000 (1 row(s) affected)
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