Can this be solved by a nested query?

Question

Hello,
Can anybody help me? Thanks a lot.
We have a test system that test production units, and output data to the TestData table in the database. The TestData table schema is like the follows. For each unit, it may pass the test system for multiple times, and each time the system generate a row of data in the table. 'Not Found' means the unit passed that time of test, no defect is found. If a defect is found the defect will be logged in the table.
The question is: I want to form a new table named TestRslt based on the TestData. The TestRslt table should be like follows, ie. each unit should have only one row of test result. For units tested with both Defect-A and Defect-B, only the row containing Defect-B will be appear in the result table. For a unit of which Defect-B is found in multiple tests, only the first time test data will be appear in the result table.
TestData
UnitID TestNumber Defect
unit-A 1 Not Found
unit-B 1 Defect-A
unit-B 2 Defect-B
unit-B 3 Not Found
unit-B 4 Defect-A
unit-C 1 Defect-B
unit-C 2 Defect-B
unit-C 3 Defect-A
TestRslt
UnitID TestNumber Defect
unit-A 1 Not Found
unit-B 2 Defect-B
unit-C 1 Defect-B

Answer 1

Hello, another alternative to get the corresponding TestNumber could be something like this:
select UnitID,
         case
            when db is not null then db
          when da is not null then da
            else d
        end d_final            
  from
    select UnitID,
             min(decode(Defect,'Defect-A',TestNumber,null)) da,
             min(decode(Defect,'Defect-B',TestNumber,null)) db,
             min(TestNumber) d
    from table
    group by UnitID
  )You can use this to join with your original table, like this:
select UnitID, TestNumber, Defect
from tabe,
       -- previous query
       (select UnitID,
                case
                   when db is not null then db
                  when da is not null then da
                   else d
               end d_final            
         from
           select UnitID,
                    min(decode(Defect,'Defect-A',TestNumber,null)) da,
                    min(decode(Defect,'Defect-B',TestNumber,null)) db,
                    min(TestNumber) d
           from table
           group by UnitID
       ) aux
where aux.unit_id = table.unit_id
      and aux.d_final = table.TestNumberI hope you could get your solution soon.