Sql – Determining a SQL Server Identity Column Name in .NET

linqlinq-to-sqlnetsql servervb.net

I'm trying to write some generic code in VB.NET that determines whether or not a SQL server database table contains an identity column and, if so, to return the name of that column.

I'm working in Visual Basic 2008 Express and have created a SQL database, "MyDatabase" with 1 table called "MyTable". Within that table, I've got 3 columns, "ID", "Column1" and "Column2". I know, I know… inventive names. Under column properties in the Database Explorer, I've set the "ID" column "Identity Specification" to "yes" and have set the "Is Identity" value to "yes".

I need for the .NET code to return "ID" as the identity column. Can this be done through LINQ or some other means?

Thanks very much in advance!

Luck

Best Answer

Use SQLDataReader to open MyTable (SELECT ID from myTable WHERE 1 = 2) & use GetSchemaTable method, which will give you the datatable.

As per the docs, check for the content of a column named IsAutoIncrement. If it returns true, it should be an Identity column.

http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqldatareader.getschematable.aspx

Note: This is purely based on my memory & help from the MSDN docs.

Syntax:

ALTER TABLE {TABLENAME} 
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL} 
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
WITH VALUES

Example:

ALTER TABLE SomeTable
        ADD SomeCol Bit NULL --Or NOT NULL.
 CONSTRAINT D_SomeTable_SomeCol --When Omitted a Default-Constraint Name is autogenerated.
    DEFAULT (0)--Optional Default-Constraint.
WITH VALUES --Add if Column is Nullable and you want the Default Value for Existing Records.

Notes:

Optional Constraint Name:
If you leave out CONSTRAINT D_SomeTable_SomeCol then SQL Server will autogenerate
a Default-Contraint with a funny Name like: DF__SomeTa__SomeC__4FB7FEF6

Optional With-Values Statement:
The WITH VALUES is only needed when your Column is Nullable
and you want the Default Value used for Existing Records.
If your Column is NOT NULL, then it will automatically use the Default Value
for all Existing Records, whether you specify WITH VALUES or not.

How Inserts work with a Default-Constraint:
If you insert a Record into SomeTable and do not Specify SomeCol's value, then it will Default to 0.
If you insert a Record and Specify SomeCol's value as NULL (and your column allows nulls),
then the Default-Constraint will not be used and NULL will be inserted as the Value.

Notes were based on everyone's great feedback below.
Special Thanks to:
@Yatrix, @WalterStabosz, @YahooSerious, and @StackMan for their Comments.

Sql – How to return only the Date from a SQL Server DateTime datatype

SELECT DATEADD(dd, 0, DATEDIFF(dd, 0, @your_date))

for example

SELECT DATEADD(dd, 0, DATEDIFF(dd, 0, GETDATE()))

gives me

2008-09-22 00:00:00.000

Pros:

No varchar<->datetime conversions required
No need to think about locale

Best Answer

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Sql – How to return only the Date from a SQL Server DateTime datatype

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