Database Release Update 19.26.0.0.250121 / 37260974

Oracle 19c RU26
EE,SE

If you place a literal in a SQL with no space between literal and columnalias, like
select 'Test'"Test1" from dual;
This wrongly works until RU24 (maybe RU25)

Since RU26 this doesn't work anymore and SQl Parser raises an error - which is correct.
03001. 00000 -  "unimplemented feature"
*Cause:    This feature is not implemented.
*Action:   None.

it has to be to corrected
select 'Test' "Test1" from dual;

It is important to know that, because maybe your sourcecode contains similar SQL which doesnt't work since RU26.

Cheers peter

Maybe Doc ID 2710359.1 explains this behaviour.

If CURSOR_SHARING is set to "SIMILAR" or "FORCE" ORA-03001 will occur. But this is since RU26 or RU25. If is set to "EXACT" it works.