Join under condition in Oracle SQL SELECT statement - sql

Question

I'm trying to join two tables under a condition but I haven't been able to make it work. I've been searching and reading but couldn't find an answer for my case.
This is the basic idea of what I'm trying to achieve (what I wrote in lowercase is what I want to achieve in my own words, in case you wonder):
SELECT TABLE1.STR_FULLNAME, TABLE1.STR_MAILBIZ, TABLE2.STR_IP
FROM TABLE1
INNER JOIN TABLE2
if TABLE2.STR_MACHINEUSER contains 'TEXT\' then join like this:
ON TABLE1.STR_LOGIN = SELECT SUBSTR(STR_MACHINEUSER, 6) AS STR_MACHINEUSER FROM TABLE2 WHERE
STR_MACHINEUSER LIKE 'TEXT\%'
else join like this:
ON TABLE1.STR_LOGIN = TABLE2.STR_MACHINEUSER
ORDER BY TABLE2.DT_INSERT DESC;
The content of Table1.STR_LOGIN and that of Table2.STR_MACHINEUSER are in some cases exactly the same and in some cases a prefix needs to be removed in Table2.STR_MACHINEUSER ('TEXT\'). I've seen that conditions should be handled with the CASE expression. I have tried different ways, but I couldn't make it work for what I need. I'm thinking that I might need a complete different approach, but I don't see what...
Does someone have a suggestion? Thanks in advance!

Answer 1

Maybe this is what you want:
SELECT TABLE1.STR_FULLNAME, TABLE1.STR_MAILBIZ, TABLE2.STR_IP
FROM TABLE1
INNER JOIN TABLE2 ON
(not TABLE2.STR_MACHINEUSER LIKE 'TEXT\%' and TABLE1.STR_LOGIN = TABLE2.STR_MACHINEUSER)
or
(TABLE2.STR_MACHINEUSER LIKE 'TEXT\%' and TABLE1.STR_LOGIN = SUBSTR(TABLE2.STR_MACHINEUSER, 6))
Sure you could shorten your statement using some case construct like:
case
when TABLE2.STR_MACHINEUSER LIKE 'TEXT\%'
then SUBSTR(TABLE2.STR_MACHINEUSER, 6) else TABLE2.STR_MACHINEUSER
end
and compare this to TABLE1.STR_LOGIN but I find (IMHO) the first (logic) join better readable.