Not sure if this is a bug, or if this is by design, but it looks very odd (at least to me).
Create an index with two descending columns, it is listed twice in table view.
CREATE TABLE DOUBLE_DESC_T (COLA NUMBER, COLB NUMBER);
CREATE INDEX DOUBLE_DESK_I ON DOUBLE_DESC_T (COLA DESC, COLB DESC);
(Note probably is same behavior in current non-EA version, no time to check right now).
This is a strange one. Due to the use of DESC on the columns in your test case, we are getting two rows returned in the top panel rather than one for the single index. Repeat your test case using...
CREATE INDEX DOUBLE_DESK_I ON DOUBLE_DESC_T (COLA, COLB);
to see what I mean. So, perhaps SQL Developer needs to issue a different query, or maybe we can consider this "expected" behavior.
So that means either dropping the COLUMN_EXPRESSION column, or concatenating those distinct row values into a single COLUMN_EXPRESSIONS value, just as we do for multi-column indexes in COLUMNS.
Bugged and fixed for 4.2 EA2.
As COLUMN_EXPRESSION is a LONG data type, the concatenation approach is not feasible. Moved it to display in the Index tab's child pane
