How to implement CASE SELECT in WHERE clause - plsql

Question

I have two tables T1 and T2
Senario 1:
Table T1 has a Column C1 with values terminal1, terminal2, terminal3
Select C1 from T1
Terminal1
Terminal2
Terminal3
Table T2 has a Column C2 with values terminal1, terminal2
Select C2 from T2
Terminal1
Terminal2
Senario 2
Table T2 can sometimes be null
Select C2 from T2
(null)
(null)
My Output has to be
When Senario 1 Then
Terminal1
Terminal2
When Senario 2 Then
Terminal1
Terminal2
Terminal3
i.e when table T1 and T2 have common values I want only the matching values
and
when Table T2 has null values then I want all the values
from table T1

Answer 1

It seems that what you need is a left outer join. Outer joins allow us to conditionally join tables.
This version of your query will return STORE_TERMINAL_LOCATION for all the rows in SP_RETAIL_TRANSACTION and matching values only of SP_TEMP_LOOKUP.AIRPORT_TERMINAL.
SELECT DISTINCT A.STORE_TERMINAL_LOCATION, B.AIRPORT_TERMINAL
FROM SP_RETAIL_TRANSACTION A,
left outer join SP_TEMP_LOOKUP B
on A.STORE_TERMINAL_LOCATION = B.AIRPORT_TERMINAL

Answer 2

Your question needs some proper formatting and elaborate more on the problem you are facing. I assume, you need a statement, which shows what values intersect, and if they do not - show only tables A. For that clause, you need to use inner joins and case structure. For example:
select
ter."HEATHROW_TERMINAL",
case
when lok."HEATHROW_TERMINAL" is not null then
'Terminal is in both tables'
else
'Terminalis only in main table'
end terminal_state
from
test_terminal_v ter,
test_lookup_v lok
where
ter."HEATHROW_TERMINAL" = lok."HEATHROW_TERMINAL"(+)
wheres, test_terminal_v (A) has values "5","4","2","3" and test_lookup_v (B) has "4","2","3".
Hope it helps.
After comments: there are several approaches. 1) You can use temporary tables. Create one and the code is:
begin
insert into test_term_tmp
select
ter.terminal
from
test_terminal_v ter,
test_lookup_v lok
where
ter.terminal = lok.terminal;
if sql%rowcount = 0 then
insert into TEST_TERM_TMP
select
ter.terminal
from
test_terminal_v ter;
end if;
end;
or 2) use types, for example:
declare
type t_term_tab is table of number index by binary_integer;
l_term t_term_tab;
l_i number := 1;
begin
for l_rec1 in (
select
ter.terminal
from
test_terminal_v ter,
test_lookup_v lok
where
ter.terminal = lok.terminal)
loop
l_term(l_i) := l_rec1.terminal;
l_i := l_i + 1;
end loop;
if l_term.first is null then
l_i := 1;
for l_rec2 in (
select
ter.terminal
from
test_terminal_v ter)
loop
l_term(l_i) := l_rec2.terminal;
l_i := l_i + 1;
end loop;
end if;
end;
Test the performance, based on your data. Hope it helps.

Answer 3

Thank you Guys, I think I found the answer
select distinct T1.C1, T2.C2
from T1 ,T2
where T2.C2=T1.C1 or T2.C2 is null;
Where in my code it was
select distinct A.STORE_TERMINAL_LOCATION,B.AIRPORT_TERMINAL
from SP_RETAIL_TRANSACTION A,SP_TEMP_LOOKUP B
where B.AIRPORT_TERMINAL=A.STORE_TERMINAL_LOCATION or B.AIRPORT_TERMINAL is null;