How can I improve this convert(int,myColumn) query? - sql-server

Question

SQL Server 2000
Background
I've got a table that stores miscellaneous meta data about a specific course in my course table. The table is defined:
create table course_prefs {
id int identity not null,
crs_nbr int references course (crs_nbr) not null,
fiscal_yr int not null,
group_name varchar(50) not null,
item_name varchar(50) null,
value varchar(100) not null)
and there are some values like so:
ID Crs_Nbr Fiscal_Yr Group_Name Item_Name Value
1 5327 2007 StuAchievement Qualifier alg
2 5329 2007 StuAchievement Qualifier alg
153 2000 2003 LocUCInfo 543 F,0,0
154 2000 2003 LocUCInfo 542 F,0,0
6149 15746 2009 summerAttn HS coreClass
6150 12367 2009 summerAttn HS coreClass
...and I've begun making views from this prefs table to suit the specific needs. However, when I join to the following view:
CREATE view loc_uc_info as
select cp.crs_nbr, c.abbr, cp.fiscal_yr, convert(int,cp.item_name) as loc_id
, substring(cp.value,1,1) as subject_area
, substring(cp.value,3,1) as honors
, substring(cp.value,5,1) as can_be_elective
from course_prefs cp join course c on cp.crs_nbr = c.crs_nbr
where cp.group_name = 'LocUCInfo'
The Problem
I get the following error message:
Syntax error converting the varchar value 'HS' to a column of data type smallint.
What I Want
I need to write a query that joins to this view on the loc_id column. This means that both the parent table and the view are joined on columns typed as integers. BUT - the view has both integer and char values in the item_name column thus, I get the syntax error. What can I do to get around this?
Things I've Tried:
Using a derived query in place of the view and I get the same error.
Creating another view based solely on the uc_loc_info view. Got same error.
Using the isnumeric(cp.item_name) = 1 where clause in my loc_uc_info view to restrict the results.

Answer 1

Not really sure what you want the outcome to be but what about using:
case when isnumeric(cp.item_name) = 1 then convert(int,cp.item_name) else null end
instead of just your
convert(int,cp.item_name)

Answer 2

Try this :
convert(int,case when isnumeric(cp.item_name)= 1 then cp.item_name else null end as loc_id
If that doesn't work try this:
convert(int,case when isnumeric(cp.item_name)= 1 then cp.item_name else 0 end as loc_id
Personally I believe something is very flawed about your basic design, you shouldn't have numerics and character data in the same column like that. Nor should you have comma delimited values.
And I'm not a fan of views, especially views that get put on top of views as they can kill performance when they can't be properly indexed.

Answer 3

Note: Final working code added below first message.
Can you explain more what you're trying to accomplish with this line in your view?
convert(int, cp.item_name) as loc_id,
Penfold's suggestion seems like a good one.
Here is working code. (Yes, it uses 2005 "sys." tables. Convert those to run on 2000.) It replaces your "loc_id" column with Penfold's suggestion.
Code
IF EXISTS (SELECT * FROM sys.tables WHERE name = 'Course')
DROP TABLE dbo.Course
GO
CREATE TABLE dbo.Course (
ID int not null, -- identity
Abbr varchar(5) not null,
Crs_Nbr int not null --references course (crs_nbr)
)
GO
IF EXISTS (SELECT * FROM sys.tables WHERE name = 'Course_Prefs')
DROP TABLE dbo.Course_Prefs
GO
CREATE TABLE dbo.Course_Prefs (
ID int not null, -- identity
Crs_Nbr int not null, --references course (crs_nbr)
Fiscal_Yr int not null,
Group_Name varchar(50) not null,
Item_Name varchar(50) null,
Value varchar(100) not null
)
GO
INSERT INTO dbo.Course VALUES (1, 'Crs1', 5327)
INSERT INTO dbo.Course VALUES (2, 'Crs2', 5329)
INSERT INTO dbo.Course VALUES (3, 'Crs3', 2000)
INSERT INTO dbo.Course VALUES (4, 'Crs4', 15746)
INSERT INTO dbo.Course VALUES (5, 'Crs5', 12367)
GO
INSERT INTO dbo.Course_Prefs VALUES (1, 5327, 2007, 'StuAchievement', 'Qualifier', 'alg')
INSERT INTO dbo.Course_Prefs VALUES (2, 5329, 2007, 'StuAchievement', 'Qualifier', 'alg')
INSERT INTO dbo.Course_Prefs VALUES (153, 2000, 2003, 'LocUCInfo', '543', 'F,0,0')
INSERT INTO dbo.Course_Prefs VALUES (154, 2000, 2003, 'LocUCInfo', '542', 'F,0,0')
INSERT INTO dbo.Course_Prefs VALUES (6149, 15746, 2009, 'summerAttn', 'HS', 'coreClass')
INSERT INTO dbo.Course_Prefs VALUES (6150, 12367, 2009, 'summerAttn', 'HS', 'coreClass')
GO
SELECT * FROM dbo.Course
SELECT * FROM dbo.Course_Prefs
GO
IF EXISTS (SELECT * FROM sys.views WHERE name = 'Loc_uc_Info')
DROP VIEW dbo.Loc_uc_Info
GO
CREATE VIEW dbo.Loc_uc_Info AS
SELECT
cp.crs_nbr,
c.abbr,
cp.fiscal_yr,
case when isnumeric(cp.item_name) = 1 then convert(int,cp.item_name) else null end AS loc_id,
--convert(int, cp.item_name) as loc_id,
substring(cp.value, 1, 1) as subject_area,
substring(cp.value, 3, 1) as honors,
substring(cp.value, 5, 1) as can_be_elective
FROM dbo.Course_Prefs AS cp
JOIN dbo.Course AS c ON cp.crs_nbr = c.crs_nbr
--WHERE cp.group_name = 'LocUCInfo'
GO
SELECT * FROM dbo.Loc_uc_Info
GO
Results
ID Abbr Crs_Nbr
----------- ----- -----------
1 Crs1 5327
2 Crs2 5329
3 Crs3 2000
4 Crs4 15746
5 Crs5 12367
ID Crs_Nbr Fiscal_Yr Group_Name Item_Name Value
----------- ----------- ----------- -------------------------------------------------- -------------------------------------------------- ----------------------------------------------------------------------------------------------------
1 5327 2007 StuAchievement Qualifier alg
2 5329 2007 StuAchievement Qualifier alg
153 2000 2003 LocUCInfo 543 F,0,0
154 2000 2003 LocUCInfo 542 F,0,0
6149 15746 2009 summerAttn HS coreClass
6150 12367 2009 summerAttn HS coreClass
crs_nbr abbr fiscal_yr loc_id subject_area honors can_be_elective
----------- ----- ----------- ----------- ------------ ------ ---------------
5327 Crs1 2007 NULL a g
5329 Crs2 2007 NULL a g
2000 Crs3 2003 543 F 0 0
2000 Crs3 2003 542 F 0 0
15746 Crs4 2009 NULL c r C
12367 Crs5 2009 NULL c r C
Edit: Forgot to include Penfold's code.
Final Working Code Based on HLGEM's Suggestion
IF EXISTS (SELECT * FROM sys.tables WHERE name = 'Course')
DROP TABLE dbo.Course
GO
CREATE TABLE dbo.Course (
ID int not null, -- identity
Abbr varchar(5) not null,
Crs_Nbr int not null --references course (crs_nbr)
)
GO
IF EXISTS (SELECT * FROM sys.tables WHERE name = 'Course_Prefs')
DROP TABLE dbo.Course_Prefs
GO
CREATE TABLE dbo.Course_Prefs (
ID int not null, -- identity
Crs_Nbr int not null, --references course (crs_nbr)
Fiscal_Yr int not null,
Group_Name varchar(50) not null,
Item_Name varchar(50) null,
Value varchar(100) not null
)
GO
INSERT INTO dbo.Course VALUES (1, 'Crs1', 5327)
INSERT INTO dbo.Course VALUES (2, 'Crs2', 5329)
INSERT INTO dbo.Course VALUES (3, 'Crs3', 2000)
INSERT INTO dbo.Course VALUES (4, 'Crs4', 15746)
INSERT INTO dbo.Course VALUES (5, 'Crs5', 12367)
GO
INSERT INTO dbo.Course_Prefs VALUES (1, 5327, 2007, 'StuAchievement', 'Qualifier', 'alg')
INSERT INTO dbo.Course_Prefs VALUES (2, 5329, 2007, 'StuAchievement', 'Qualifier', 'alg')
INSERT INTO dbo.Course_Prefs VALUES (153, 2000, 2003, 'LocUCInfo', '543', 'F,0,0')
INSERT INTO dbo.Course_Prefs VALUES (154, 2000, 2003, 'LocUCInfo', '542', 'F,0,0')
INSERT INTO dbo.Course_Prefs VALUES (6149, 15746, 2009, 'summerAttn', 'HS', 'coreClass')
INSERT INTO dbo.Course_Prefs VALUES (6150, 12367, 2009, 'summerAttn', 'HS', 'coreClass')
GO
SELECT * FROM dbo.Course
SELECT * FROM dbo.Course_Prefs
GO
IF EXISTS (SELECT * FROM sys.views WHERE name = 'Loc_uc_Info')
DROP VIEW dbo.Loc_uc_Info
GO
CREATE VIEW dbo.Loc_uc_Info AS
SELECT
cp.crs_nbr,
c.abbr,
cp.fiscal_yr,
convert(int,
case
when isnumeric(cp.item_name) = 1 then cp.item_name
else 0
end
) as loc_id,
substring(cp.value, 1, 1) as subject_area,
substring(cp.value, 3, 1) as honors,
substring(cp.value, 5, 1) as can_be_elective
FROM dbo.Course_Prefs AS cp
JOIN dbo.Course AS c ON cp.crs_nbr = c.crs_nbr
WHERE cp.group_name = 'LocUCInfo'
GO
SELECT * FROM dbo.Loc_uc_Info
GO

Answer 4

Just from the top of my head: What about creating two views?
One that does the join without converting and another one that just does the conversion on the first view.
Since the first view should only contain numbers in the Item_Name (namely 543 and 542) you will not have the conversion error.