How to Select a substring in Oracle SQL up to a sp

Question

Say I have a table column that has results like:

ABC_blahblahblah
DEFGH_moreblahblahblah
IJKLMNOP_moremoremoremore

I would like to be able to write a query that selects this column from said table, but only returns the substring up to the Underscore (_) character. For example:

ABC
DEFGH
IJKLMNOP

The SUBSTRING function doesn't seem to be up to the task because it is position-based and the position of the underscore varies.

I thought about the TRIM function (the RTRIM function specifically):

SELECT RTRIM('listofchars' FROM somecolumn) 
FROM sometable

But I'm not sure how I'd get this to work since it only seems to remove a certain list/set of characters and I'm really only after the characters leading up to the Underscore character.

Answer 1

Another possibility would be the use of REGEXP_SUBSTR.