indexing - SQL/Oracle: when indexes on multiple columns can be used -

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if create index on columns (a, b, c), in order, understanding database able use if search on (a), or (a , b), or (a , b , c), not if search on (b), or (c), or (b , c). correct?

there 3 index-based access methods oracle can use when predicate placed on non-leading column of index.

i) index skip-scan: http://download.oracle.com/docs/cd/b19306_01/server.102/b14211/optimops.htm#pfgrf10105

ii) fast full index scan: http://download.oracle.com/docs/cd/b19306_01/server.102/b14211/optimops.htm#i52044

iii) index full scan: http://download.oracle.com/docs/cd/b19306_01/server.102/b14211/optimops.htm#i82107

i've seen fast full index scan "in wild", possible.


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