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Applies to: 
 SQL Server 
 Azure SQL Database 
 Azure SQL Managed Instance 
 Azure Synapse Analytics 
 Analytics Platform System (PDW) 
 SQL analytics endpoint in Microsoft Fabric 
 Warehouse in Microsoft Fabric
A function that returns the angle, in radians, whose tangent is a specified float expression. This is also called arctangent.
 Transact-SQL syntax conventions
Syntax
ATAN ( float_expression )  
Arguments
float_expression
An expression of either type float or of a type that implicitly convert to float.
Return types
float
Examples
This example takes a float expression and returns the ATAN of the specified angle.
SELECT 'The ATAN of -45.01 is: ' + CONVERT(varchar, ATAN(-45.01))  
SELECT 'The ATAN of -181.01 is: ' + CONVERT(varchar, ATAN(-181.01))  
SELECT 'The ATAN of 0 is: ' + CONVERT(varchar, ATAN(0))  
SELECT 'The ATAN of 0.1472738 is: ' + CONVERT(varchar, ATAN(0.1472738))  
SELECT 'The ATAN of 197.1099392 is: ' + CONVERT(varchar, ATAN(197.1099392))  
GO  
Here's the result set.
  
-------------------------------   
The ATAN of -45.01 is: -1.54858                         
  
(1 row(s) affected)  
  
--------------------------------   
The ATAN of -181.01 is: -1.56527                         
  
(1 row(s) affected)  
  
--------------------------------   
The ATAN of 0 is: 0                                
  
(1 row(s) affected)  
  
----------------------------------   
The ATAN of 0.1472738 is: 0.146223                         
  
(1 row(s) affected)  
  
-----------------------------------   
The ATAN of 197.1099392 is: 1.56572                          
  
(1 row(s) affected)  
Examples: Azure Synapse Analytics and Analytics Platform System (PDW)
This example takes a float expression and returns the arctangent of the specified angle.
SELECT ATAN(45.87) AS atanCalc1,  
    ATAN(-181.01) AS atanCalc2,  
    ATAN(0) AS atanCalc3,  
    ATAN(0.1472738) AS atanCalc4,  
    ATAN(197.1099392) AS atanCalc5;  
Here's the result set.
atanCalc1  atanCalc2  atanCalc3  atanCalc4  atanCalc5
---------  ---------  ---------  ---------  ---------
1.55       -1.57       0.00       0.15       1.57
See also
CEILING (Transact-SQL)
Mathematical Functions (Transact-SQL)