How to count null values in postgresql?

问题

select distinct "column" from table;

output:

    column
1     0.0
2     [null]
3     1.0

But when I try to count the null values

select count("column") from train where "column" is NULL;

Gives output 0 (zero)

Can you suggest where it's going wrong?

回答1:

Use count(*):

select count(*) from train where "column" is NULL;

count() with any other argument counts the non-NULL values, so there are none if "column" is NULL.

来源：https://stackoverflow.com/questions/53934294/how-to-count-null-values-in-postgresql