Jon asks:
> Can anyone shed any light on why using like instead of = on one column
> should cause such a significant slow down (45secs / 0.4 secs)?
A query involving a LIKE operator can only use an index if the wildcard(s)
are placed after an initial constant string. The initial constant string
is what is looked up in the index; wildcard matching is done with either
a scan of the relevant part of the index or with a full table scan.
Cheers,
Colin