how to compare values in two columns of two different tables using cursor - sql

Question

declare
v_column varchar2(100);
v_incident_id number;
v_check_incident varchar2(100);
v_check_audit varchar2(100);
query_str varchar2(1000);
cursor c1 is
select COLUMN_NAME
from ALL_TAB_COLUMNS
where upper(TABLE_NAME)=upper('Incidents');
begin
open c1;
loop
fetch c1 into v_column;
exit when c1%notfound;
select incident_id into v_incident_id from incident_audit;
DBMS_OUTPUT.PUT_LINE('incident column: '||v_column);
select v_column
into v_check_incident
from incidents
where incident_id= v_incident_id;
select to_char(v_column)
into v_check_audit
from incident_audit
where incident_id=v_incident_id;
DBMS_OUTPUT.PUT_LINE('incident column: '||v_check_incident);
DBMS_OUTPUT.PUT_LINE('audit column : '||v_check_audit);
if(v_check_incident != v_check_audit)
then
DBMS_OUTPUT.PUT_LINE('inside insert');
insert into PHIIT_AUD(AUDIT_ID ,INCIDENT_ID,OLD_VALUE,NEW_VALUE,UPDATED_BY,UPDATED_ON,COLUMN_NAME)
values(audit_id_seq.nextval,v_incident_id,v_check_audit,v_check_incident,NVL(v('APP_USER'),USER),sysdate,v_column);
end if;
end loop;
DBMS_OUTPUT.PUT_LINE('Total number of rows : '||c1%ROWCOUNT);
close c1;
end;
Problem: Getting Column names from ALL_TAB_COLUMNS in cursor and using it to compare with the other column of other table
output : incident column: INCIDENT_ID
incident column: INCIDENT_ID
audit column : INCIDENT_ID
incident column: BUSINESS_UNIT_ID
incident column: BUSINESS_UNIT_ID
audit column : BUSINESS_UNIT_ID
The cursor is returning value as column_name instead of its value in order to compare.

Answer 1

"The cursor is returning value as column_name "
Of course it is, that's what you're telling it to do. select v_column from incidents means select the value in the variable.
What you need to do is use Dynamic SQL to create a select statement which substitutes the value in the variable for a column name: 'select '||v_column||' from incidents' .
Here is the sort of thing you need to do.
declare
v_column varchar2(100);
v_incident_id number;
v_check_incident varchar2(100);
v_check_audit varchar2(100);
query_str varchar2(1000);
cursor c1 is
select COLUMN_NAME
from ALL_TAB_COLUMNS
where upper(TABLE_NAME)=upper('Incidents');
rc sys_refcursor;
begin
open c1;
loop
fetch c1 into v_column;
exit when c1%notfound;
select incident_id into v_incident_id from incident_audit;
DBMS_OUTPUT.PUT_LINE('incident column: '||v_column);
-- dynamic SQL
open rc for
'select'|| v_column ||
' from incidents where incident_id= :1'
using v_incident_id;
fetch rc into v_check_incident;
close rc;
open rc for
'select'|| v_column ||
' from incident_audit where incident_id= :1'
using v_incident_id;
fetch rc into v_check_audit;
close rc;
DBMS_OUTPUT.PUT_LINE('incident column: '||v_check_incident);
DBMS_OUTPUT.PUT_LINE('audit column : '||v_check_audit);
if(v_check_incident != v_check_audit)
then
DBMS_OUTPUT.PUT_LINE('inside insert');
insert into PHIIT_AUD(AUDIT_ID ,INCIDENT_ID,OLD_VALUE,NEW_VALUE,UPDATED_BY,UPDATED_ON,COLUMN_NAME)
values(audit_id_seq.nextval,v_incident_id,v_check_audit,v_check_incident,NVL(v('APP_USER'),USER),sysdate,v_column);
end if;
end loop;
DBMS_OUTPUT.PUT_LINE('Total number of rows : '||c1%ROWCOUNT);
close c1;
end;
I have kept it close to your original implementation so you can understand the principle. However, I think this is a poor implementation which will be very inefficient if you have lots of audits to verify. But addressing that is a different matter.