Need help to get alternate or better way to write query

Question

Hi,
I am on Oracle 11.2
DDL and sample data
create table tab1 -- 1 millions rows at any given time
id       number       not null,
ref_cd   varchar2(64) not null,
key      varchar2(44) not null,
ctrl_flg varchar2(1),
ins_date date
create table tab2 -- close to 100 million rows
id       number       not null,
ref_cd   varchar2(64) not null,
key      varchar2(44) not null,
ctrl_flg varchar2(1),
ins_date date,
upd_date date
insert into tab1 values (1,'ABCDEFG', 'XYZ','Y',sysdate);
insert into tab1 values (2,'XYZABC', 'DEF','Y',sysdate);
insert into tab1 values (3,'PORSTUVW', 'ABC','Y',sysdate);
insert into tab2 values (1,'ABCDEFG', 'WYZ','Y',sysdate);
insert into tab2 values (2,'tbVCCmphEbOEUWbxRKczvsgmzjhROXOwNkkdxWiPqDgPXtJhVl', 'ABLIOWNdj','Y',sysdate);
insert into tab2 values (3,'tbBCFkphEbOEUWbxATczvsgmzjhRQWOwNkkdxWiPqDgPXtJhVl', 'MQLIOWNdj','Y',sysdate);I need to get all rows from tab1 that does not match tab2 and any row from tab1 that matches ref_cd in tab2 but key is different.
Expected Query output
'ABCDEFG',  'WYZ'
'XYZABC',   'DEF'
'PORSTUVW', 'ABC'Existing Query
select
   ref_cd,
   key
from
    select
        ref_cd,
        key
    from
        tab1, tab2
    where
        tab1.ref_cd = tab2.ref_cd and
        tab1.key    <> tab2.key
    union
    select
        ref_cd,
        key
    from
        tab1
    where
        not exists
           select 1
           from
               tab2
           where
               tab2.ref_cd = tab1.ref_cd
    );I am sure there will be an alternate way to write this query in better way. Appreciate if any of you gurus suggest alternative solution.
Thanks in advance.

Answer 1

Hi,
user572194 wrote:
... DDL and sample data ...
create table tab2 -- close to 100 million rows
id       number       not null,
ref_cd   varchar2(64) not null,
key      varchar2(44) not null,
ctrl_flg varchar2(1),
ins_date date,
upd_date date
insert into tab2 values (1,'ABCDEFG', 'WYZ','Y',sysdate);
insert into tab2 values (2,'tbVCCmphEbOEUWbxRKczvsgmzjhROXOwNkkdxWiPqDgPXtJhVl', 'ABLIOWNdj','Y',sysdate);
insert into tab2 values (3,'tbBCFkphEbOEUWbxATczvsgmzjhRQWOwNkkdxWiPqDgPXtJhVl', 'MQLIOWNdj','Y',sysdate);
Thanks for posting the CREATE TABLE and INSERT statments. Remember why you go to all that trouble: so the people whop want to help you can re-create the problem and test their ideas. When you post statemets that don't work, it's just a waste of time.
None of the INSERT statements for tab2 work. Tab2 has 6 columns, but the INSERT statements only have 5 values.
Please test your code before you post it.
I need to get all rows from tab1 that does not match tab2 WHat does "match" mean in this case? Does it mean that tab1.ref_cd = tab2.ref_cd?
and any row from tab1 that matches ref_cd in tab2 but key is different.
Existing Query
select
ref_cd,
key
from
select
ref_cd,
key
from
tab1, tab2
where
tab1.ref_cd = tab2.ref_cd and
tab1.key    <> tab2.key
union
select
ref_cd,
key
from
tab1
where
not exists
select 1
from
tab2
where
tab2.ref_cd = tab1.ref_cd
Does that really work? In the first branch of the UNION, you're referencing a column called key, but both tables involved have columns called key. I would expect that to cause an error.
Please test your code before you post it.
Right before UNION, did you mean
tab1.key    != tab2.key? As you may have noticed, this site doesn't like to display the &lt;&gt; inequality operator. Always use the other (equivalent) inequality operator, !=, when posting here.
I am sure there will be an alternate way to write this query in better way. Appreciate if any of you gurus suggest alternative solution.Avoid UNION; it can be very inefficient.
Maybe you want something like this:
SELECT       tab1.ref_cd
,       tab1.key
FROM           tab1
LEFT OUTER JOIN  tab2  ON  tab2.ref_cd     = tab1.ref_cd
WHERE       tab2.ref_cd  IS NULL
OR       tab2.key     != tab1.key
;