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?
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
.
Some workaround when you want to count the values on aggregations, including NULL ones, but can't use count(*)
(if other columns are different too).
On these cases, you can use this request :
count(distinct("column")) + (CASE bool_or("column" is null) WHEN true THEN 1 ELSE 0 END)
The count(distinct(column))
will count the non null values, and the other part will add 1
if there is a null value
Use SUM
SELECT SUM(CASE WHEN column IS NULL THEN 1 ELSE 0 END) AS column_null_tally
FROM table;
您得到零是因为您正在计算空(空)值,您需要计算非空字段中的值,例如 id 字段。
select count("id_column") from train where "data_column" is NULL;
SELECT
COUNT(*) FILTER (WHERE "column" IS NULL) AS is_null,
COUNT(*) FILTER (WHERE "column" < 1.0) AS lt_one,
COUNT(*) FILTER (WHERE "column" > 1.0) AS gt_one,
COUNT(*) FILTER (WHERE "column" = 1.0) AS just_perfect
FROM "table";
Since
select count(coalesce(t."column", 0)) from table t
is the full number with NULL:s and select count(t."column") from table t
is the number without NULL:s, this works as well:
Select count(coalesce(t."column", 0)) - count(t."column") FROM table t;
(This answer might also help those who came here to count both NULL and not NULL, at least I was stranded here since I was searching for that) .
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