sql question

my relation works as follows...

serial_number is linked to job_number is linked to
product_nubmer (ie, job_number_id in serial number
table and product_id in job_number table).

the following query makes sense to me...

select t_serial_number.serial_number_id,
t_serial_number.serial_number
from t_serial_number, t_job_number, t_product
where t_product.product_id=2

however, this query also works...

select t_serial_number.serial_number_id,
t_serial_number.serial_number
from t_serial_number, t_product
where t_product.product_id=2

the difference is i ommitted any mention of the table
that links product to serial number (ie,
t_job_number).

which query is faster? is the latter query ok to use
in a production environment or is the former query
"safer?"

also, in pgadmin, the query view clock (lower right)
is in the form of 10+20ms. what does this "time"
format mean?

tia...

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