Query optimization and indexes

Suppose I have an index on 5 columns (A, B, C, D, E).

If my WHERE clause is not in that order, will the optimizer reorder
them as necessary and possible?

WHERE A=1 AND C=3 AND B=2 AND E=5 AND D=4

Obviously it can't reorder them in all cases:

WHERE A=1 AND (C=3 OR B=2) AND (E=5 OR D=4)

If I don't specify columns in the WHERE clause, how much can it use
the index? I think it is smart enough to use beginning columns:

WHERE A=1 AND B=2

How about skipping leading columns?

WHERE B=2

How about skipping intermediate columns?

WHERE A=1 AND C=3

Or both, which is probably the same?

WHERE B=2 AND D=4?

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Felix Finch: scarecrow repairman & rocket surgeon / felix(at)crowfix(dot)com
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