Re: [SQL] DISTINCT count(*), possible?

Another way is

SELECT DISTINCT field INTO temp_table FROM mytable;
SELECT count(*) FROM temp_table;
DROP TABLE temp_table;

which is arguably more efficient than the previous solution
for large tables --- it should involve O(n log n) work rather
than O(n^2). For a small table, the overhead of creating and
dropping a table might overshadow the actual work, though.

In 6.5 you can use "INTO TEMP temp_table" and avoid worrying
about having to invent distinct temp table names for concurrent
users of the database.

The SQL-standard "SELECT count(DISTINCT field)" would be even nicer,
of course, but I dunno when someone will get around to it...

regards, tom lane