I was under the impression that an index like
CREATE NONCLUSTERED INDEX IX_Name_Age ON People ( Name ASC, Age ASC )
would be used not only for a query like Select * From People WHERE Name = 'X' and Age = Y but would also function as a single-column index for something like Select * From People WHERE Name = 'Z'
However, in my few tests I've done so far, that doesn't seem to be the case. For example, I have an index on Manufacturer/PartNumber with Manufacturer as the leading column, but a Select * WHERE Manufacturer = 'A' still does a table scan.
Am I doing/interpreting something incorrectly or was my initial assumption wrong?