FIX: Nonclustered Index Not Chosen with Varchar and LIKE Clause

• Microsoft SQL Server version 7.0

SYMPTOMS

On large tables, a nonclustered index covering the WHERE clause is not chosen if a varchar field is specified by a LIKE clause.

RESOLUTION

A supported fix that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem. If you are not severely affected by this specific problem, Microsoft recommends that you wait for the next SQL Server service pack that contains this fix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

http://www.microsoft.com/support/supportnet/overview/overview.asp

   Version    File name     Platform
   ---------------------------------

   7.00.706   S70706I.EXE   Intel
   7.00.706   S70706A.EXE   Alpha 

WORKAROUND

When possible, replace the nonclustered index covered by the WHERE clause with a clustered index. In the example given in the MORE INFORMATION section of this article, you would change the primary key clustered index by a nonclustered index. Re-create index [BUT000~SOT] as clustered.

STATUS

Microsoft has confirmed this to be a problem in SQL Server version 7.0.

MORE INFORMATION

The following script will reproduce the problem:

drop table BUT000
go
create table BUT000
(CLIENT varchar(3) NOT NULL, PARTNER varchar(10) NOT NULL,
 BPEXT varchar(22) NOT NULL, MCNAME varchar(32) NOT NULL,
 BU_SORT1 varchar(21) NOT NULL, BU_SORT2 varchar (21) NOT NULL)
Go
alter table BUT000
add constraint [BUT000~0]
primary key clustered (CLIENT, PARTNER)
go
create nonclustered index [BUT000~EXT] on BUT000 (CLIENT, BPEXT)
go
create nonclustered index [BUT000~NAM] on BUT000 (CLIENT, MCNAME)
go
create nonclustered index [BUT000~SOT] on BUT000 (CLIENT, BU_SORT1,BU_SORT2)
go

-- Primary Key violations occur during the table load
-- due to the usage of the rand function
declare @counter1 int
declare @counter2 int
declare @counter3 int
declare @counter4 int
declare @var2 varchar(32)

set nocount on
set @counter1 = 1
set @counter3 = 0
set @counter2 = 40000
set @counter4 = convert(int, rand() * 32)


set @var2 = char(convert(int,(rand()*26)) + 65)
          + char(convert(int,(rand()*26)) + 65)
          + char(convert(int,(rand()*26)) + 65) + 'JTH'

while @counter1 < 600000
begin
	select @counter3 = @counter2
	while @counter4 > 0
	begin
		insert into BUT000
            values ('260', convert(varchar, @counter3),'', @var2,'','')
		set @counter3 = @counter3 +1 
		set @counter4 = @counter4 -1
		set @counter1 = @counter1 + 1
	end
	set @var2 = char(convert(int,(rand()*26)) + 65)
                + char(convert(int,(rand()*26)) + 65)
                + char(convert(int,(rand()*26)) + 65)
                + 'JTH'
	set @counter2 = @counter2 + convert(int,rand()*10000)
	set @counter4 = convert(int, rand() * 32)
end 

select * from BUT000 where CLIENT ='260' and MCNAME like ' MCK%' 

Additional query words:

Keywords : SSrvTran_SQL kbbug7.00 kbSQLServ700bug
Version : winnt:7.0
Platform : winnt
Issue type : kbbug