I am confused reading statements in "Why is 1899-12-30 the zero date in Access / SQL Server instead of 12/31?"
Was there date type in SQL Server before 2008 version? I cannot find.
In SQL Server 2008 zero date is 0001-01-01. Were there any date type before (in previous SQL Server versions) how is it backward compatible?
No. Prior to SQL Server 2008, there was only the datetime and smalldatetime types.
Data type...............Range..................................................................Accuracy
datetime..................January 1, 1753, through December 31, 9999.....3.33 milliseconds
smalldatetime..........January 1, 1900, through June 6, 2079............... 1 minute
Please see: Date and Time Data in SQL Server 2008, specifically the bit that says "Date/Time Data Types Introduced in SQL Server 2008"
In SQL Server datetime datatype the minimum date that can be stored is 1 Jan 1753.
However the datetimes are stored as numeric offsets to a base date of 1900-01-01 00:00:00.000
SELECT CAST(-0.25 AS DATETIME) /*1899-12-31 18:00:00.000*/
SELECT CAST(0 AS DATETIME) /*1900-01-01 00:00:00.000*/
SELECT CAST(0.25 AS DATETIME) /*1900-01-01 06:00:00.000*/
1899-12-30 has no significance in SQL Server.
SELECT CAST(CAST('1899-12-30' AS DATETIME) AS FLOAT) /*Returns -2*/