log-transact-sql.md

title	LOG (Transact-SQL) | Microsoft Docs
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ms.date	07/29/2017
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LOG (Transact-SQL)

[!INCLUDEtsql-appliesto-ss2008-all_md]

Returns the natural logarithm of the specified float expression in [!INCLUDEssNoVersion].

Transact-SQL Syntax Conventions

Syntax

-- Syntax for SQL Server  
  
LOG ( float_expression [, base ] )  

-- Syntax for Azure SQL Database, Azure SQL Data Warehouse, Parallel Data Warehouse  
  
LOG ( float_expression )  

Arguments

float_expression
Is an expression of type float or of a type that can be implicitly converted to float.

base
Optional integer argument that sets the base for the logarithm.

Applies to: [!INCLUDEssSQL11] through [!INCLUDEssCurrent]

Return Types

float

Remarks

By default, LOG() returns the natural logarithm. Starting with [!INCLUDEssSQL11], you can change the base of the logarithm to another value by using the optional base parameter.

The natural logarithm is the logarithm to the base e, where e is an irrational constant approximately equal to 2.718281828.

The natural logarithm of the exponential of a number is the number itself: LOG( EXP( n ) ) = n. And the exponential of the natural logarithm of a number is the number itself: EXP( LOG( n ) ) = n.

Examples

A. Calculating the logarithm for a number.

The following example calculates the LOG for the specified float expression.

DECLARE @var float = 10;  
SELECT 'The LOG of the variable is: ' + CONVERT(varchar, LOG(@var));  
GO  

[!INCLUDEssResult]

-------------------------------------  
The LOG of the variable is: 2.30259  
  
(1 row(s) affected)  

B. Calculating the logarithm of the exponent of a number.

The following example calculates the LOG for the exponent of a number.

SELECT LOG (EXP (10));  
  

[!INCLUDEssResult]

----------------------------------  
10  
(1 row(s) affected)  

Examples: [!INCLUDEssSDWfull] and [!INCLUDEssPDW]

C. Calculating the logarithm for a number

The following example calculates the LOG for the specified float expression.

SELECT LOG(10);  

[!INCLUDEssResult]

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

2.30

D. Calculating the logarithm of the exponent of a number

The following example calculates the LOG for the exponent of a number.

SELECT LOG(EXP (10));  

[!INCLUDEssResult]

---------

10.00

See Also

Mathematical Functions (Transact-SQL)
EXP (Transact-SQL)
LOG10 (Transact-SQL)