I have a reasonable sized table (~2m rows), with an indexed field for which
there are ~200 possible values.
I want a quick way to find out if there are any rows matching a specified
value for this indexed field. I dont care how many there are or what their
properties are, just if there are any or not.
Here's a quick example:
CREATE TABLE mytable(c1 INT4 PRIMARY KEY, c2 INT2);
CREATE INDEX myindex ON mytable(c2);
SELECT COUNT(c2) AS num FROM mytable WHERE c2=1234;
The time it takes to execute the above query appears to be of the order O(n)
- is there an O(1) query to do it - given that I only want to know if num>0
or if num=0? (the function COUNT() doesn't have to be used).
Any help appreciated,