Add pivot table to table seach about anemometer

[gtowey]

ouch, the hard part is to make this support custom fields for which pivots are much harder to write. For example:

A pivot on Query_time_sum column in the table would result in an expression like:
SUM(IF(hostname_max='host', Query_time_sum, 0)))

But an expression like the average query time SUM(Query_time_sum) / SUM(ts_cnt) is much harder. It would have to be something like:
SUM(IF(hostname_max='host', Query_time_sum, 0))) / SUM(IF(hostname_max='host', ts_cnt, 0)))

Each aggregate function would have to be turned into an IF()

The question is if we can do that kind of parsing reliably.

One idea is to require that custom fields define their own pivot operation -- otherwise they cannot be used.