Sql-server – Why does OBJECT_ID return NULL in a computed column

sql serversql-server-2008t-sqltempdb

I'm trying to produce a usage report for some stored procedures in my database. The view view sys.dm_exec_procedure_stats contains some of what I need, so I decided to start here.

SQL Server keys procedure metadata by object ID. I know only the procedure names, so first I have to map the names to IDs using the OBJECT_ID function.

There are several procedures to check, so I want to put their names in a temp table before processing them.

I thought it would be cute to get the object id from a computed column in the temp table, so I created a table like this:

USE msdb;

  name SYSNAME,
  [object_id] AS OBJECT_ID(name)

INSERT INTO #procs (name) VALUES ('dbo.sp_send_dbmail');
INSERT INTO #procs (name) VALUES ('dbo.sp_add_job');
INSERT INTO #procs (name) VALUES ('dbo.sp_start_job');

With that table in place, the obvious way to get the execution counts looked like this:

SELECT #procs.name, execution_count
FROM sys.dm_exec_procedure_stats AS procstats
INNER JOIN #procs ON #procs.[object_id] = procstats.[object_id]
ORDER BY execution_count DESC;

But it returns an empty result set!

This query shows why the result set is empty:

SELECT name, [object_id]
FROM #procs;

The object_id column is NULL, so an inner join will produce no rows:

name                 object_id
-------------------- -----------
dbo.sp_send_dbmail   NULL
dbo.sp_add_job       NULL
dbo.sp_start_job     NULL

It's not that computed columns are broken for temp tables. If I add a computed column to reverse the name, it produces the correct value when I select from it:

ALTER TABLE #procs ADD reverse_name AS REVERSE(name);

SELECT name, [object_id], reverse_name
FROM #procs;


name                 object_id   reverse_name
-------------------- ----------- ---------------------
dbo.sp_send_dbmail   NULL        liambd_dnes_ps.obd
dbo.sp_add_job       NULL        boj_dda_ps.obd
dbo.sp_start_job     NULL        boj_trats_ps.obd

Why does OBJECT_ID return NULL here?

Best Answer

A metadata function mentioned in a computed column in a #temp table is going to reference tempdb.sys.objects, not yourdatabase.sys.objects, since the table is created in tempdb. Try adding the database prefix to the insert, and that will make OBJECT_ID go find it in the right place:

  name SYSNAME,
  [object_id] AS OBJECT_ID(name)

INSERT INTO #procs (name) VALUES ('dbo.sp_send_dbmail');
INSERT INTO #procs (name) VALUES ('msdb.dbo.sp_send_dbmail');

SELECT name, [object_id] FROM #procs;


dbo.sp_send_dbmail          NULL
msdb.dbo.sp_send_dbmail     283148054