SQL Count Magic Required....

i have the following query that yields a series of
true or false results:

-- distinct on is pgsql extension --
SELECT DISTINCT ON (t_inspect_result.inspect_id)
t_inspect_result.inspect_result_id,

t_inspect_result.inspect_result_pass,
                   t_inspect_area.inspect_area,

t_inspect_result.inspect_result_timestamp
                   --,t_inspect.serial_number_id,
t_inspect.inspect_id
FROM t_inspect_result, t_inspect, t_inspect_area,
     t_serial_number,
t_link_contract_number_job_number, t_job_number,
t_product
WHERE  t_inspect.inspect_area_id =
       t_inspect_area.inspect_area_id
AND t_inspect.serial_number_id =
    t_serial_number.serial_number_id
AND t_serial_number.link_contract_number_job_number_id
=

t_link_contract_number_job_number.link_contract_number_job_number_id
AND t_link_contract_number_job_number.job_number_id =
    t_job_number.job_number_id
AND t_product.product_id =
    t_job_number.product_id
AND t_inspect.inspect_id =
    t_inspect_result.inspect_id
AND t_inspect.serial_number_id = '200'
ORDER BY t_inspect_result.inspect_id DESC,
t_inspect_result.inspect_result_timestamp ASC
-- used to get first pass yield pass / fail (true /
false) data.
-- inspect_id desc impacts end result.  time desc
impacts the groups prior to being distinctly listed

the simplified output may look like

f,t,t,f,f,f,t,f,t,f

the COUNT magic comes into play b/c i want to count
the result set's "t"s and total, but i have no clue
how to get this done.

#ts: 4
#total: 10

when i have this data, i can apply some math and come
up with a 40% yield.

any help is, as always, much appreciated.

tia...

ps - this query looks to be brutal when there is a lot
of data.  is it?  if so, how can i optimize it?

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