Re: How does Oracle use indexes?

Rick,

A vendor has supplied an application with the following three indexes on a table:-

Index1 uses columns col1, col2, col3, col4, col5, col6.
Index2 uses columns col1, col2, col3.  
Index3 uses columns col1, col2.

You are absolutely right, in your scenario, index2 and index 3 are reduntant. In a composite index, also known as a concatenated index, if you have a 5 column index the index will be used in V6 if the where clause references all or the leading portion of the columns in the composite index.

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Ray Dutcher
Oracle DBA
Xerox Corp.
1350 Jefferson Rd., 801-15A
Rochester, NY 14623