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SQL Server 2008 R2 : Creating and Managing Stored Procedures - Deferred Name Resolution

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In SQL Server 2008, the object names that a stored procedure references do not have to exist at the time the procedure is created. SQL Server 2008 checks for the existence of database objects at the time the stored procedure is executed and returns an error message at runtime if the referenced object doesn’t exist. The only exception is when a stored procedure references another stored procedure that doesn’t exist. In that case, a warning message is issued, but the stored procedure is still created (see Listing 1).
Listing 1. Procedure Name Resolution During Stored Procedure Creation
create proc p2
as
exec p3
go

The module 'p2' depends on the missing object 'p3'. The module will still be
  created; however, it cannot run successfully until the object exists.


					  

When a table or view does exist at procedure creation time, the column names in the referenced table are validated. If a column name is mistyped or doesn’t exist, the procedure is not created (see Listing 2).

Listing 2. Column Name Validation in Stored Procedures
IF EXISTS ( SELECT * FROM sys.procedures
               WHERE schema_id = schema_id('dbo')
                 AND name = N'get_authors_and_titles')
   DROP PROCEDURE dbo.get_authors_and_titles
GO
create proc get_authors_and_titles
as

select a.au_lname, au_fname, title, isbn_number
   from authors a join titleauthor ta on a.au_id = ta.au_id
   join titles t on t.title_id = ta.title_id
return
go

Server: Msg 207, Level 16, State 1, Procedure get_authors_and_titles, Line 4
Invalid column name 'isbn_number'.


					  

One advantage of delayed (or deferred) name resolution is the increased flexibility when creating stored procedures; the order of creating procedures and the tables they reference does not need to be exact. Delayed name resolution is an especially useful feature when a stored procedure references a temporary table that isn’t created within that stored procedure. However, at other times, it can be frustrating to have a stored procedure create successfully only to have it fail when it runs due to a missing table, as shown in Listing 3.

Listing 3. Runtime Failure of a Stored Procedure with an Invalid Object Reference
create proc get_authors_and_titles
as

select a.au_lname, au_fname, title, pub_date
   from authors a join titleauthor ta on a.au_id = ta.au_id
   join books t on t.title_id = ta.title_id

go

EXEC get_authors_and_titles
go

Server: Msg 208, Level 16, State 1, Procedure get_authors_and_titles, Line 4
 Invalid object name 'books'.


					  

Another issue to be careful of with deferred name resolution is that you can’t rename objects referenced by stored procedures and have the stored procedure continue to work. In versions of SQL Server prior to 7.0, after the stored procedure was created, object references within the stored procedure were made via the object ID rather than the object name. This allowed stored procedures to continue to function properly if a referenced object was renamed. However, now that object names are resolved at execution time, the procedure fails at the statement referencing the renamed object. For the stored procedure to execute successfully, it needs to be altered to specify the new object name.

Identifying Objects Referenced in Stored Procedures

Because changing the name of a table can cause stored procedures to no longer work, you might want to identify which stored procedures reference a specific table so you know which stored procedures will be affected by changes to the table name or columns. You can view the dependencies between database objects by querying the sys.sql_dependencies object catalog view. Unfortunately, all you really see if you query the sys.sql_dependencies view is a bunch of numbers—just the IDs of the objects and columns that have a dependency relationship, along with some additional status information.

The better way to display a list of stored procedures that reference a specific table or view, or to display a list of objects referenced by a stored procedure, is to use the sys.dm_sql_referencing_entities and sys.dm_sql_referenced_entities dynamic management functions.

sys.dm_sql_referencing_entities ( ' schema_name.table_or_view_name ' , ' OBJECT ' )
sys.dm_sql_referenced_entities ( ' schema_name.proc_name ' , ' OBJECT ' )


					  

For example, to display the stored procedures, triggers, functions, and views that reference the titles table, you would execute the following:

select referencing_schema_name, referencing_entity_name
 From sys.dm_sql_referencing_entities ( 'dbo.titles' , 'OBJECT' )
go

In the bigpubs2008 database, the titles table is referenced by the following:

referencing_schema_name   referencing_entity_name
-------------------------------------------------
dbo                       AverageBookPrice
dbo                       AverageBookPrice2
dbo                       AveragePricebyType
dbo                       AveragePricebyType2
dbo                       reptq1
dbo                       reptq2
dbo                       reptq3
dbo                       title_authors
dbo                       titleview
dbo                       valid_book_types

To display the objects referenced by the title_authors stored procedure, you could execute the following:

select distinct
     referenced_entity_name as table_name,
     referenced_minor_name as column_name
 From sys.dm_sql_referenced_entities ('dbo.title_authors' , 'OBJECT' )
go

In the current database, the specified object references the following:

table_name      column_name
----------------------------
authors         NULL
authors         au_fname
authors         au_id
authors         au_lname
titleauthor     NULL
titleauthor     au_id
titleauthor     title_id
titles          NULL
titles          title
titles          title_id

You can also see dependency information in SSMS by right-clicking an object and choosing View Dependencies. This brings up the Object Dependencies window, as shown in Figure 1. You can view either the objects that depend on the selected object or objects on which the selected object depends. You can also expand the dependency tree for the objects listed in the Dependencies pane.

Figure 1. Viewing object dependencies in SSMS.
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