SQL query to find columns having at least one non null value

I am developing a data validation framework where I have this requirement of checking that the table fields should have at least one non-null value i.e they shouldn’t be completely empty having all values as null.

For a particular column, I can easily check using

select count(distinct column_name) from table_name;

If it’s greater than 0 I can tell that the column is not empty. I already have a list of columns. So, I can execute this query in the loop for every column but this would mean a lot of requests and it is not the ideal way.

What is the better way of doing this? I am using Microsoft SQL Server.

Answer

I would not recommend using count(distinct) because it incurs overhead for removing duplicate values. You can just use count().

You can construct the query for counts using a query like this:

select count(col1) as col1_cnt, count(col2) as col2_cnt, . . .
from t;

If you have a list of columns you can do this as dynamic SQL. Something like this:

declare @sql nvarchar(max);

select @sql = concat('select ',
                     string_agg(concat('count(', quotename(s.value), ') as cnt_', s.value),
                      ' from t'
                    )
from string_split(@list) s;

exec sp_executesql(@sql);

This might not quite work if your columns have special characters in them, but it illustrates the idea.