If you ever looked at the dynamic management views or one of the system catalogs in SQL Server a column called Object ID will be associated, from the looks of it this number doesn’t actually relate to anything – but there is actually a lot more to it than that. Object_ID is a unique id number for an object within the database, this is used internally by SQL Server. It should be noted, not all objects have an object_id. DDL triggers for example do not as they are not schema-scoped.
If we run a query against sys.columns, lots of information will be returned about all the columns in the database.
SELECT * FROM sys.columns
However, the result set will look something like this:
object_id | name | column_id ….
4 rowsetid 1
4 rowsetcolid 2
151671588 MiddleName 4
While the column name is in readable text, the object_id isn’t actually anything useful (to a human). In fact, this is the ID of the table which the column belongs to. In order to get the name of the object from the object_id there is a function called Object_Name(). This will take the object_id and return a readable name. If we re-run the query but including the object_name
SELECT OBJECT_NAME(object_id) as TableName, * FROM sys.columns
Then the table name is returned in a helpful manner.
TableName | object_id | name | column_id ….
sysrowsetcolumns 4 rowsetid 1
sysrowsetcolumns 4 rowsetcolid 2
vEmployee 151671588 MiddleName 4
We could also use the Object_ID() function to obtain the object_id for an object in database. For example, the query below asks for the object_id for the Customers table in Northwind. This returns 21575115
Of course, flipping this around will return us Customers again.
There is also a similar function when you are given a schema_id. Schema_Name() works in the same fashion but returns the schema name based on the Schema_Id.
SELECT OBJECT_NAME(object_id), SCHEMA_NAME(schema_id), * FROM sys.tables
Hopefully this will clear up what Object_ID is. I know next time I query one of SQL Server tables I will be able to return at least some more meaningful information.