Why OBJECT_ID used while checking if a table exists or not

Question

I need to check if a table in SQL exist or not.

If not it must create one automatically.

Now I researched and found this code:

IF  NOT EXISTS (SE         


        

Answer 1

object_id = OBJECT_ID(N'[dbo].[YourTable]')

object_id is the column name in sys.objects

OBJECT_ID is a function that returns the ID for the object you specify, i.e. YourTable.

You are comparing the object_id of YourTable with the object_id column in the sys.objects table. You need to replace YourTable with the table name you want to check already exists.

Answer 2

OBJECT_ID() is a function which returns the Object ID. See the documentation:

Returns the database object identification number of a schema-scoped object.

http://msdn.microsoft.com/en-us/library/ms190328.aspx

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By passing it certain parameters (ie. your table details), it will return an ID. You can then compare this with the IDs in the sys.objects table to check whether it currently exists.

Answer 3

The ISO SQL way to check existence of a table level object is the INFORMATION_SCHEMA.TABLES view

There's nothing wrong with looking at sys.objects but.... INFORMATION_SCHEMA.TABLES is a bit more declarative -- and it's cross platform (which often doesn't matter at all but meh still nice.)

I think this is probably more readable for a new coder though:

DECLARE @tableName SYSNAME = 'tbfoo'
DECLARE @schemaNAme SYSNAME = 'fooSchema'

IF EXISTS ( SELECT 1 FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = @tableName AND TABLE_SCHEMA = @schemaName )
BEGIN
    RAISERROR('%s exists in schema: %s', 0, 1, @tableName, @schemaName)
END
ELSE
BEGIN
    RAISERROR('%s DOES NOT EXIST in schema: %s', 0, 1, @tableName, @schemaName)
END

Don't worry about the RAISERROR command -- its just a nice way of printing formatted messages.

You can query the INFORMATION_SCHEMA view to get a sense of what's in it.

SELECT TOP 5 * FROM INFORMATION_SCHEMA.TABLES

As you can see -- you can reference schemas and catalogs by name rather than looking up their ID with OBJECT_ID()

Answer 4

I like this syntax:

if(object_id(N'[dbo].[YourTable]', 'U') is not null)
...

Where object_id takes the 2 char type of object as the second parameter. You can find the list of Object types listed below in the sys.objects documentation:

• 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
• 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