Clustered index - multi-part vs single-part index and effects of inserts/deletes
- by Anssssss
This question is about what happens with the reorganizing of data in a clustered index when an insert is done. I assume that it should be more expensive to do inserts on a table which has a clustered index than one that does not because reorganizing the data in a clustered index involves changing the physical layout of the data on the disk. I'm not sure how to phrase my question except through an example I came across at work.
Assume there is a table (Junk) and there are two queries that are done on the table, the first query searches by Name and the second query searches by Name and Something. As I'm working on the database I discovered that the table has been created with two indexes, one to support each query, like so:
--drop table Junk1
CREATE TABLE Junk1
(
Name char(5),
Something char(5),
WhoCares int
)
CREATE CLUSTERED INDEX IX_Name ON Junk1
(
Name
)
CREATE NONCLUSTERED INDEX IX_Name_Something ON Junk1
(
Name, Something
)
Now when I looked at the two indexes, it seems that IX_Name is redundant since IX_Name_Something can be used by any query that desires to search by Name. So I would eliminate IX_Name and make IX_Name_Something the clustered index instead:
--drop table Junk2
CREATE TABLE Junk2
(
Name char(5),
Something char(5),
WhoCares int
)
CREATE CLUSTERED INDEX IX_Name_Something ON Junk2
(
Name, Something
)
Someone suggested that the first indexing scheme should be kept since it would result in more efficient inserts/deletes (assume that there is no need to worry about updates for Name and Something). Would that make sense? I think the second indexing method would be better since it means one less index needs to be maintained.
I would appreciate any insight into this specific example or directing me to more info on maintenance of clustered indexes.
