Question: In PSQL, I want to declare a Cursor within cursor. The second cursor should use a value from the first cursor in the "where clause". How can I do this?
Answer: Below is an example of how to declare a cursor within a cursor.
In this example, we have a cursor called get_tables that retrieves the owner and table_name values. These values are then used in a second cursor called get_columns.
create or replace procedure MULTIPLE_CURSORS_PROC is
v_owner varchar2(40);
v_table_name varchar2(40);
v_column_name varchar2(100);
/* First cursor */
cursor get_tables is
select distinct tbl.owner, tbl.table_name
from all_tables tbl
where tbl.owner = 'SYSTEM';
/* Second cursor */
cursor get_columns is
select distinct col.column_name
from all_tab_columns col
where col.owner = v_owner
and col.table_name = v_table_name;
begin
-- Open first cursor
open get_tables;
loop
fetch get_tables into v_owner, v_table_name;
open get_columns;
loop
fetch get_columns into v_column_name;
end loop;
close get_columns;
end loop;
close get_tables;
EXCEPTION
WHEN OTHERS THEN
raise_application_error(-20001,'An error was encountered - 'SQLCODE' -ERROR- 'SQLERRM);
end MULTIPLE_CURSORS_PROC;
The trick to declaring a cursor within a cursor is that you need to continue to open and close the second cursor each time a new record is retrieved from the first cursor. That way, the second cursor will use the new variable values from the first cursor.
