如何选择仅在另一列中包含空值的分组行？

Question

It's a bit confusing, so I'll try to exemplify in the table below:

example-table

id	data1	data2	data3
1	NULL	NULL	NULL
1	NULL	NULL	NULL
2	1	NULL	1
2	1	NULL	NULL
2	1	NULL	1
3	1	NULL	NULL
3	1	NULL	1
4	NULL	NULL	NULL

So, grouping by the same ID, I only want to display those IDs that all their data, from all columns, are null. In the table example above, only IDs 1 and 4.

The code I'm trying to use - just for reference:

select id
from example-table
group by id, data1, data2, data3
having data1 is null and data2 is null and data3 is null; 

Any suggestions?

Answer 1

You can group by id only and set the conditions in the HAVING clause:

SELECT id
FROM tablename
GROUP BY id
HAVING COALESCE(MAX(data1), MAX(data2), MAX(data3)) IS NULL;