Mihai Gheorghiu wrote:
> What runs faster?
> select where timestamp IS NOT NULL
> or
> select where boolean IS TRUE?
It depends..... (You knew somebody would say that, didn't you? :-))
If you return a lot of data, then the statement that returns the least data is likely to be the fastest.
Otherwise, on my 6M+ records test database, it seems to be about the same. Maybe the boolean select is a little faster
real 0m12.969s
user 0m0.020s
sys 0m0.000s
vs.
real 0m13.326s
user 0m0.000s
sys 0m0.010s
for four records returned?
>
> Does it make a significant difference if the boolean is indexed? There are
> many records in the table.
Not if there are about even number of the values, but if there is only a few of the one you search for, it will help a
lot. In my test it reduces the query time to
real 0m0.315s
user 0m0.010s
sys 0m0.000s
for the first query and
real 0m0.038s
user 0m0.010s
sys 0m0.000s
when it is repeated (and the index presumably is cached in memory)
--- Allan.
