MySQL-如何返回不同的ID，其中相同ID的所有行的字段值均为空

Question

I have a query with two joins that returns this data:

ID Score
1 NULL
1 5
1 6
2 NULL
2 NULL
3 5
3 8
3 3
3 NULL
3 NULL
3 7
4 NULL
4 NULL
4 3
4 9

I would like to return the unique IDs which have a NULL value in the Score column for each of the rows with the same ID. In this case, the query should only return one row with the ID of 2 since that is the only ID which has all NULL values in the Score column.

Thank you!

Answer 1

You could aggregate your original query by making it as a sub select and aplly count() on score column which has null values, So if all values are NULL for a particular ID then count will return 0, thus using having clause you can filter your results using result of count(Score)

select ID,
  count(Score) count_null 
from (your query)t
group by ID
having count_null = 0

Demo Based on your sample data set