§
Indexes
are special lookup tables that the database search engine can use to speed up
data retrieval.
§ An
index can be created in a table to find data more quickly and efficiently.
§ An
index helps speed up SELECT queries and WHERE clauses, but it slows down data
input, with UPDATE and INSERT statements.
§ Indexes
can be created or dropped with no effect on the data.
§ Updating
a table with indexes takes more time than updating a table without (because the
indexes also need an update).
Clustered indexes
§ Uses
physical memory.
§ Easy
to retrieve data.
§ Data
is in stored form.
Non-clustered indexes
§ No use of
physical memory is needed.
§ More
complicated, data retrieval is not that easy.
§
We can
toocreateuniqueindex.Duplicatevalues are not
allowed.
CREATEINDEXindex_name
ONtable_name(column_name)
CREATEINDEXindex_name
ONtable_name(column_name)
CREATEINDEXPindex
Difference
between clustered index and non-clustered index
Clustered index
|
Non-clustered index
|
One table can only
have one clustered index
|
It can have more than one non clustered index
|
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