second argument of function OBJECT_ID

Question

I have encountered the following code in the book "TSQL Fundamentals" by Itzik Ben-Gan.

I understand that the function OBJECT_ID is used to check whether a particular object exists or not. However I'm a bit confused by its second argument N'U'.

I looked up MSDN documentation and it says that the second argument represents the object type, but I still dont understand what N'U' stands for.

Could someone please explain it to me what it actually represents?

IF OBJECT_ID(N'dbo.Employees', N'U') IS NOT NULL
BEGIN
    IF OBJECTPROPERTY(OBJECT_ID(N'dbo.Employees', N'U'), N'TableTemporalType') = 2
        ALTER TABLE dbo.Employees SET(SYSTEM_VERSIONING = OFF);

Answer 1

If you follow the link in the page you linked to types: sys.objects

U = Table (user-defined)

**Complete list (as of 2017-01-16)**

Object type:

AF = Aggregate function (CLR)
C  = CHECK constraint
D  = DEFAULT (constraint or stand-alone)
F  = FOREIGN KEY constraint
FN = SQL scalar function
FS = Assembly (CLR) scalar-function
FT = Assembly (CLR) table-valued function
IF = SQL inline table-valued function
IT = Internal table
P  = SQL Stored Procedure
PC = Assembly (CLR) stored-procedure
PG = Plan guide
PK = PRIMARY KEY constraint
R  = Rule (old-style, stand-alone)
RF = Replication-filter-procedure
S  = System base table
SN = Synonym
SO = Sequence object

 Applies to: SQL Server 2012 through SQL Server 2016.

SQ = Service queue
TA = Assembly (CLR) DML trigger
TF = SQL table-valued-function
TR = SQL DML trigger
TT = Table type
U  = Table (user-defined)
UQ = UNIQUE constraint
V  = View
X  = Extended stored procedure

 Applies to: SQL Server 2016 through SQL Server 2016, Azure SQL
Database, Azure SQL Data Warehouse, Parallel Data Warehouse.

ET = External Table

Answer 2

SELECT DISTINCT type,type_desc FROM sys.objects

type type_desc
---- ------------------------------------------------------------
TT   TYPE_TABLE
FN   SQL_SCALAR_FUNCTION
SN   SYNONYM
IF   SQL_INLINE_TABLE_VALUED_FUNCTION
UQ   UNIQUE_CONSTRAINT
SQ   SERVICE_QUEUE
F    FOREIGN_KEY_CONSTRAINT
U    USER_TABLE
D    DEFAULT_CONSTRAINT
PK   PRIMARY_KEY_CONSTRAINT
V    VIEW
S    SYSTEM_TABLE
IT   INTERNAL_TABLE
P    SQL_STORED_PROCEDURE
TF   SQL_TABLE_VALUED_FUNCTION