Notes on GetSchemaTable

I recent found myself using the SqlDataReader.GetSchemaTable method. I made some notes detailing what it will return for various data types in SQL Server 2005.

Notes on GetSchemaTable

			Numeric
ColumnName	DataType	ColumnSize	Precision	Scale	Notes
bigint	Int64	8	19	255
bit	Boolean	1	255	255
decimal	Decimal	17	18	0
int	Int32	4	10	255
money	Decimal	8	19	255
numeric	Decimal	17	18	0
smallint	Int16	2	5	255
smallmoney	Decimal	4	10	255
tinyint	Byte	1	3	255
float	Double	8	15	255
real	Single	4	7	255
datetime	DateTime	8	23	3
smalldatetime	DateTime	4	16	0
char	String	20	255	255
varchar	String	20	255	255
text	String	2147483647	255	255	isLong
nchar	String	20	255	255
nvarchar	String	20	255	255
varchar(max)	String	2147483647	255	255	isLong
nvarchar(max)	String	2147483647	255	255	isLong
ntext	String	1073741823	255	255	isLong
timestamp	Byte[]	8	255	255	IsRowVersion
xml	String	2147483647	255	255	isLong

I created these notes through the simple method of creating a table with every possible data type. Or rather, every data type that I am interested in, which is very nearly the same thing--I mean, who uses varbinary, really? I then used the GetSchemaTable method on my new table, and inspected the results.

There is a page on MSDN that appears to contain this information, but upon closer inspection, it must be talking about something else entirely. For instance, it claims that the SQL Server data type "varchar" has no mapping whatsoever, not even as a System.String.

Certainly, this makes sense upon further reflection: it's possible to put any varchar value into a string, but not the other way around. Still, it's not terribly useful if you just want to know what sort of data type you can reasonably expect to get out of a given column.

I further note that the MSDN documentation states that the NumericPrecision column should be null for non-numeric data types, but this is simply not true.