Does a multi-column index eliminate the need for a single column index?

[tec-4]

Hi Everyone,

 

If I had an index covering multiple columns would I need to have a separate single column index for the "root" column? Or does it being the main column in the multi-column index work just as well?

 

For example, say i have the following index on these columns, and in this order: (County, Status, Type, SubType)

 

Would having a single column index on County be of any benefit or simply a waste of space?

 

Please let me know if I need to elaborate further or if more info is needed to make a correct decision.

 

Thanks for the help!

[fenway]

You are correct -- there is no benefit to having a single column index when you a multi-field index and the single column is the first in the mulit-column index.