Microsoft SQL Server version number

SQL Server 2019 -> 15.0.X.X

SQL Server 2017 -> 14.0.X.X
SQL Server 2016 -> 13.0.X.X
SQL Server 2014 -> 12.0.X.X
SQL Server 2012 -> 11.0.X.X
SQL Server 2008 R2 -> 10.50.X.X
SQL Server 2008 -> 10.0.X.X
SQL Server 2005 -> 9.0.X.X


Program Files\Microsoft SQL Server\MSSQL.n\MSSQL\LOG\ERRORLOG 
Select @@version 
SELECT
SERVERPROPERTY('ProductLevel') AS ProductLevel,
SERVERPROPERTY('ProductUpdateLevel') AS ProductUpdateLevel,
SERVERPROPERTY('ProductBuildType') AS ProductBuildType,
SERVERPROPERTY('ProductUpdateReference') AS ProductUpdateReference,
SERVERPROPERTY('ProductVersion') AS ProductVersion,
SERVERPROPERTY('ProductMajorVersion') AS ProductMajorVersion,
SERVERPROPERTY('ProductMinorVersion') AS ProductMinorVersion,
SERVERPROPERTY('ProductBuild') AS ProductBuild
GO

More details : 

https://en.wikipedia.org/wiki/History_of_Microsoft_SQL_Server