[转帖]decimal and numeric (Transact-SQL)

https://learn.microsoft.com/en-us/sql/t-sql/data-types/decimal-and-numeric-transact-sql?view=sql-server-ver16

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance Azure Synapse Analytics Analytics Platform System (PDW) SQL Endpoint in Microsoft Fabric Warehouse in Microsoft Fabric

Numeric data types that have fixed precision and scale. Decimal and numeric are synonyms and can be used interchangeably.

Arguments

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 identical to decimal.

p (precision)
The maximum total number of decimal digits to be stored. This number includes both the left and the right sides of the decimal point. The precision must be a value from 1 through the maximum precision of 38. The default precision is 18.

Note

Informatica only supports 16 significant digits, regardless of the precision and scale specified.

s (scale)
The number of decimal digits that are 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. Scale must be a value from 0 through p, and can only be specified if precision is specified. The default scale is 0 and so 0 <= s <= p. Maximum storage sizes vary, based on the precision.

Precision	Storage bytes
1 - 9	5
10-19	9
20-28	13
29-38	17

Note

Informatica (connected through the SQL Server PDW Informatica Connector) only supports 16 significant digits, regardless of the precision and scale specified.

Converting decimal and numeric data

For decimal and numeric data types, SQL Server considers each 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 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. Conversely, if the SET ARITHABORT option is ON, SQL Server raises an error when overflow occurs. Loss of only precision and scale isn't sufficient to raise an error.

Prior to SQL Server 2016 (13.x), conversion of float values to decimal or numeric is restricted to values of precision 17 digits only. Any float value less than 5E-18 (when set using either the scientific notation of 5E-18 or the decimal notation of 0.000000000000000005) rounds down to 0. This is no longer a restriction as of SQL Server 2016 (13.x).

Examples

The following example creates a table using the decimal and numeric data types. Values are inserted into each column. The results are returned by using a SELECT statement.

SQLCopy

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.

SQLCopy

MyDecimalColumn                         MyNumericColumn

--------------------------------------- ---------------------------------------

123.00                                  12345.12000  

(1 row(s) affected)