Case Decode - invalid column name error

Question

select Workweek, max( decode( Type, T34, prct, null ) ) Bad,
                    max( decode( Type, T35, prct, null ) ) Repair,
                    max( decode( Type, T36, prct, null ) ) Good
FROM
(select Workweek, Type, round(ratio_to_report(sum(Testtime_in_Minutes)) over(partition by Workweek)*100,3) prct
FROM
(select ts.lot as Lot, ts.wafer_id as Wafer, dt.SORT_X as X, dt.SORT_Y as Y, ts.devrevstep as PRODUCT, ts.operation as OPERATION, dt.INTERFACE_BIN as INTERFACE_BIN, (dt.TEST_TIME)/60.0 as Testtime_in_Minutes,
ts.TEST_END_DATE_TIME as Test_End_Time, ts.Program_Name, ts.test_end_work_week as Workweek,
(CASE
WHEN (dt.INTERFACE_BIN > 9 AND dt.INTERFACE_BIN < 15) THEN 'T34'
WHEN (dt.INTERFACE_BIN =30 OR dt.INTERFACE_BIN =31 OR dt.INTERFACE_BIN = 32 OR dt.INTERFACE_BIN = 33) THEN 'T35'
     ELSE 'T36'
     END ) Type
from a_testing_session ts, a_device_testing dt
where ts.test_end_work_week >= 200715
and (ts.devrevstep like '9600%')
and dt.lao_start_ww = ts.test_end_work_week
and dt.ts_id = ts.ts_id)
GROUP BY Workweek, Type)
This sql query above does not run properly, gives invalid column name error. However, the entire select statement surrounded by the () works. There must be an error in the first 4 lines someplace, but I do not see it.

Answer 1

Assuming type is a string, I assume you meant
MAX( DECODE( type, 'T34', prct, NULL )) Badwhere T34 is a string literal. Otherwise, you'd need to have columns named T34, T35, and T36 in your inner select.
One note, though, it's probably a bad idea to have a column named Type. While it's legal to do so, TYPE is a keyword in SQL, so that name will at a minimum be confusing.
Justin