ANS : ADVANTAGES :-
A secondary index may be created and dropped dynamically
It can be created on any column be it unique or not unique.
A table may consists of up to 32 secondary indexes
DISADVANTAGES :
They require additional i/o to maintain their sub-tables.
If the statistics are not collected properly then the ptimiger goes for a full table scan
There is always an overhead for additional spaces, since there no sub-tables to be created
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