plsql List all table.column containing null values - sql

Question

I'd like to find all column of a set of table with null values in them.
I can find the table and column names
SELECT TABLE_NAME, COLUMN_NAME
FROM user_tab_cols
where nullable='Y'
and table_name in ('myTalbe', 'myTable2');
And also check if the are nulls
select count(*) from myTable where myColumn is null;
but how can I put this toghether to have as result
table_name column_name
myTable myColumn
myTable myCol2
myTable2 col4

Answer 1

An approach could be with some dynamic SQL, but this would require some PL/SQL code; the following only uses SQL to get the result you need:
select *
from (
select table_name,
column_name,
to_number(extractvalue(xmltype(dbms_xmlgen.getxml('select count(*) c from '||table_name || ' where ' || column_name || ' is null')),'/ROWSET/ROW/C')) as rowcount
from user_tab_columns
where nullable='Y'
and table_name in ('myTalbe', 'myTable2')
)
where rowcount > 0
This could be an approach with dynamic SQL:
declare
type tableOfNumber is table of number;
type tableOfChar is table of varchar2(30);
--
vSQl varchar2(4000);
vListNumbers tableOfNumber;
vListTables tableOfChar;
vListColumns tableOfChar;
begin
select listagg( 'select ''' ||
table_name || ''' as table_name, ''' ||
column_name || ''' as column_name, count(*) as rowCount from ' ||
table_name ||
' where ' ||
column_name ||
' is null having count(*) > 0' ,
' UNION ALL '
) within group ( order by table_name, column_name)
into vSQL
from user_tab_columns
where nullable='Y'
and table_name in ('myTalbe', 'myTable2');
--
dbms_output.put_line(vSQL);
/* whatever you may want to do with the query */
/* for example, fetch into some variables and print the result */
execute immediate vSQL
bulk collect into vListTables, vListColumns, vListNumbers;
--
if vListTables.count() > 0 then
for i in vListTables.first .. vListTables.last loop
dbms_output.put_line('Table ' || vListTables(i) ||
', column ' || vListColumns(i) ||
', number of nulls: ' || vListNumbers(i)
);
end loop;
end if;
end;

Answer 2

Here's a routine I wrote a while back to do exactly that. It will output the required DDL to make those columns that are nullable (but do not contain any nulls) not nullable.
https://connormcdonald.wordpress.com/2016/03/11/tightening-up-your-data-model/
It can do the task for a schema or a single table.