I would like an explanation of what a clustered index is and the other
types of indexes in SQL Server.
I really don't understand the differences or their significance,
especially in relation to what I have known for years on VFP indexes.
You seem to be quite a pro in SQL Server so can you help?
TIA
Rafael Copquin
El 14/11/2013 14:41, Stephen Russell escribió:
Stealing from a Tips book or white paper.
SELECT * is not always a bad thing, but it’s a good idea
to only move the data you really need to move and only
when you really need it, in order to avoid network, disk,
and memory contention on your server.
For small sets of data that are
infrequently updated such as lookup
values, build a method of caching
them in memory on your application
server rather than constantly querying
them in the database.
*--**- this is a big one in that every DB has the same problem.
A function on columns in the WHERE clause or JOIN
criteria means that SQL Server can’t use indexes
appropriately and will lead to table scans and slow
performance.
Avoid using a column in a clustered index that has
values that are frequently updated.
You do not have to make the primary key the clustered
index. This is default behavior but can be directly
controlled.
Clustered indexes work well on columns that are used
a lot for ‘range’ WHERE clauses such as BETWEEN and
LIKE, where it is frequently used in ORDER BY clauses
or in GROUP BY clauses.
If you join to a Date|Time table adding that dtmAdded column to the primary
key is very helpful and if you filter on that column it will greatly help
your throughput.
Only create non-clustered indexes on tables when you
know they’ll be used through testing. You can seriously
hurt performance by creating too many indexes on a
table.
While it is possible to over-normalize a database,
under-normalization is much more prevalent. This
leads to repetition of data, inefficient storage, and poor
performance. Data normalization is a performance
tuning technique as well as a storage mechanism.
All from Red Gate.
Stephen Russell
Sr. Analyst
Ring Container Technology
Oakland TN
901.246-0159 cell
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