different results using count(x)

Hello,


What's the difference between:

SELECT count(id) FROM scanns WHERE tipus='esc'; => 11235
SELECT count(pages) FROM scanns WHERE tipus='esc'; => 11165
SELECT count(*) FROM scanns WHERE tipus='esc'; => 11235

Why are some rows that aren't included in the count(pages) SELECT ?

There are not NULL values in the pages field:

SELECT count(pages) FROM scanns WHERE tipus='esc' AND pages IS NOT
NULL; => 11165
SELECT count(pages) FROM scanns WHERE tipus='esc' AND pages IS NULL;
=> 0

And I think the three SELECTS should return the same rows number ...


thanks for your help,

r.