Having some trouble with indexes on sql server 2005. I'll explain it with a simplified example.
I have a customers table, and a sp to list customers :
create table Customers(
CusID int not null,
Name varchar(50) null,
Surname varchar(50) null,
CusNo int not null,
Deleted bit not null
)
create proc spCusLs (
@.CusID int = null,
@.Name varchar(50) = null,
@.Surname varchar(50) = null,
@.CusNo int = null
)
as
select
CusID,
Name,
Surname,
CusNo
from
Customers
where
Deleted = 0
and CusID <> 1000
and (@.CusID is null or CusID = @.CusID)
and (@.CusNo is null or CusNo = @.CusNo)
and (@.Name is null or Name like @.Name)
and (@.Surname is null or Surname like @.Surname)
order by
Name,
Surname
create nonclustered index ix_customers_name on customers ([name] asc)
with (sort_in_tempdb = off, drop_existing = off, ignore_dup_key = off, online = off) on primary
create nonclustered index ix_customers_surname on customers (surname asc)
with (sort_in_tempdb = off, drop_existing = off, ignore_dup_key = off, online = off) on primary
create nonclustered index ix_customers_cusno on customers (cusno asc)
with (sort_in_tempdb = off, drop_existing = off, ignore_dup_key = off, online = off) on primary
I've recently noticed that some tables, including 'Customers' don't have indexes except primary keys. And I have added indexes to "name", "surname" and "cusno" columns. This has dropped the number of IO reads. But the strange thing is; one time it works with name / surname searches like ('joh%' '%') but when CusNo is included, it does a full scan. And vice versa when the SP is recompiled using 'alter', works ok with CusNo, but not with name/surname. Recompile it, and it's reversed again. When run as a single query, the execution plan looks different.
What's happening? Perhaps something to do with statistics? This doesn't have a big payload on the server, but there are some other procs suffering from this on heavy queries, making server performance worse than before...
You will get the best performance if you can create a "covering" index for this query, which is a non-clustered index that includes all of the columns needed to satisfy or "cover" the query.
In this case, I would try a unique, non-clustered index on Deleted, CusID, CusNo, Name, and SurName (all of these in a single NC index). You may have to play around with the order of the columns in this index (based on their selectivity) to get the best results.
Also, the fact that you are using OR and LIKE in your WHERE clause will cause performance issues. I would consider splitting this into two SP's instead of trying to use an "all-purpose" SP for this.
sql