ur qstn is unambigious

Try STUFF string function…

REgards,
NandaKumar

Umesh

As it is being said “Besides, this Primary Key may not be used in Joins.”

It is quite possible that other tables having foreign key referring the primarykey(let it be non Identity column which you have created separately and declared it as pk)

So PK mostly be used as foreign key which can appear in joins also as well as in where clause to filter the records.

so whats the point to create separate column as pk and not to use identity columns as pk?

-Anil

If both indexes, clustered and non-clustered are ordered in the same way then there’s probably no benefit from non-clustered index.

But I’ve heard that in some cases having two indexes ordered in opposite ways will increase performance for select queries.

Also if I use multiple fields in the join/where then I’ll add composite indexes to the table that may overlap with existing ones.

But anyway, always measure your performance after you’ve done changes. For instance, I did some changes to a DB last week and I’m planning to spend part of next week to observe how those changes are affecting the whole software, not just that table.

I don’t think it is a great idea to create a clustered as well as nonclustered indexes on the same column. as the clustered index will be having a reference to all the columns in the table but the nonclustered index will only have a reference to the columns specified.

The key point here is that whenever You update or delete a row (or column)

all the index will be updated.
It is redundant to have two indexes on a column.

In Your case the indexes will take nearly twice time to update, so more time on locks on table.

So a big performance hit.

I have to gracefully disagree and exactly for the points you make against using IDENTITY as PK.

> There is no use of this Primary Key in both application and in T-SQL

That is exactly why I always prefer adding “separate” IDENTITY column as PK. I don’t want to ever show PK values outside the DB. If I need to expose PK outside I make sure in the application code that it is only seen in the data acces layer.

> Besides, this Primary Key may not be used in Joins.

But does it matter? You can use other column in joins and build unique index to those. You just have to make sure you don’t kill performance with additional indexes, of course. If I use PK column in joins or in where-clause, I usually add non-clustered index to it also.

I am not able to get the concept regarding the following point that you have specified:

Please note that many database experts suggest that it is not a good practice to make Identity Column as Primary Key. The reason behind this suggestion is that many times Identity Column that has been assigned as Primary Key does not play any role in database. There is no use of this Primary Key in both application and in T-SQL. Besides, this Primary Key may not be used in Joins. It is a known fact that when there is JOIN on Primary Key or when Primary Key is used in the WHERE condition it usually gives better performance than non primary key columns. This argument is absolutely valid and one must make sure not to use such Identity Column.

Please explain it more clearly regarding the above point.

Thanks,
Santosh