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ROUND (Transact-SQL)

SQL Server 2008

Returns a numeric value, rounded to the specified length or precision.

Topic link iconTransact-SQL Syntax Conventions

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ROUND (numeric_expression , length [ ,function ] )
numeric_expression

Is an expression of the exact numeric or approximate numeric data type category, except for the bit data type.

length

Is the precision to which numeric_expression is to be rounded. length must be an expression of type tinyint, smallint, or int. When length is a positive number, numeric_expression is rounded to the number of decimal positions specified by length. When length is a negative number, numeric_expression is rounded on the left side of the decimal point, as specified by length.

function

Is the type of operation to perform. function must be tinyint, smallint, or int. When function is omitted or has a value of 0 (default), numeric_expression is rounded. When a value other than 0 is specified, numeric_expression is truncated.

Returns the following data types.

Expression result

Return type

tinyint

int

smallint

int

int

int

bigint

bigint

decimal and numeric category (p, s)

decimal(38, s)

money and smallmoney category

money

float and real category

float

ROUND always returns a value. If length is negative and larger than the number of digits before the decimal point, ROUND returns 0.

Example

Result

ROUND(748.58, -4)

0

ROUND returns a rounded numeric_expression, regardless of data type, when length is a negative number.

Examples

Result

ROUND(748.58, -1)

750.00

ROUND(748.58, -2)

700.00

ROUND(748.58, -3)

1000.00

A. Using ROUND and estimates

The following example shows two expressions that demonstrate by using ROUND the last digit is always an estimate.

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SELECT ROUND(123.9994, 3), ROUND(123.9995, 3)
GO

Here is the result set.

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----------- -----------
123.9990    124.0000

B. Using ROUND and rounding approximations

The following example shows rounding and approximations.

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SELECT ROUND(123.4545, 2);
GO
SELECT ROUND(123.45, -2);
GO

Here is the result set.

----------

123.4500

(1 row(s) affected)

--------

100.00

(1 row(s) affected)

C. Using ROUND to truncate

The following example uses two SELECT statements to demonstrate the difference between rounding and truncation. The first statement rounds the result. The second statement truncates the result.

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SELECT ROUND(150.75, 0);
GO
SELECT ROUND(150.75, 0, 1);
GO

Here is the result set.

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--------
151.00

(1 row(s) affected)

--------
150.00

(1 row(s) affected)
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Annotations FAQ
This does not explain the rounding algorithm
More specifically, why would 15934.70855 be rounded as 15934.7085 instead of 15934.7086 ?
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Incorrect Example
In remarks->example: ROUND(748.58, -3) will return an error when ran. An Arthimetic overflow will be returned.
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