Finding Columns with only NULL as values

Question

I have a list of tables around 30 in number. Among them i need to generate a report with Table Name and Column Names, for which all values are NULL.
In other words, i need to find all the columns for which all the values are NULL.
I thought of dealing it with cursors, and comparing the total count with null count in each column. But i need to loop "Number of columns" times. Is there any better way to do this?

Answer 1

I think your way is a good solution. It has the advantage that you can check several columns in one select.
select count(*), count(col1), count(col2) ... from mytabAnother approach could be to check statistical information about your table data.
However this will not give you always the correct data.
It depends on the time of the last statistic collection, the sample size and on the detail level.
Here is a sample statement to play with:
select owner, table_name, column_name, num_distinct, num_nulls, num_buckets, sample_size, low_value, high_value
from all_tab_columns
where owner not in ('SYS','SYSTEM')
and nullable = 'Y' -- null values allowed
and num_distinct = 0 -- only nulls found
--and density = 0
;Note that this select would not return tables for which no statistics had been calculated. Num_distinct is NULL in such a case.
Edited by: Sven W. on Feb 11, 2010 2:50 PM