Will sql server create any default non-clustered index? Should we really put all FK as non-clustered index? What is the trade-off here
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No, SQL Server does not automatically create non-clustered indexes.
A clustered index is created automatically based on the primary key, unless your CREATE TABLE statement says otherwise.
Yes, I would recommend indexing foreign key columns because these are the most likely to be JOIN'd/searched against using IN, EXISTS, etc. However, be aware that an index on a low cardinality set of values (gender for example) will be relatively useless because there's not enough difference in the values.
The trade-off with all indexes is that they can speed up data retrieval, but slow down data insertion/updating/deletion. There's also maintenance that needs to be performed because they can get fragmented (like hard drives) but also might not get used over time. Indexes also take up drive space.
2 Comments
Praneeth
thanks...What happens if there is non-clustered key and no non-clustered key on FK that i am using it to join with the child table. What scan does it use? Full, Index seek and Index scan?
OMG Ponies
Depends on the query, the index, the table statistics & the optimizer -- it means looking at the explain plan.