SQL & PL/SQL :: Find Top 20 Most Occurred Words In Particular Text Column

My requirment is to find the top 20 most occurred words in the perticular text column accross the full table. i WILL have desc column which is plain text where user wites the essay. i have below 2 data example where i have 2 find which word occur most of the time. i have more than 1 million data where i have to perfor this calculation

E.g
INCIDENT_NOINITIAL_SD_FAULT_DESC 70000030 late entering service on the outer rail causing a 4 minute delay. After speaking to the Hainault DDM and the Hainault DMT it has been established that 70000031E105 on entering into platform by one cars lenght applied emergency brakes to stop the train due to a person under his train. Train stopped with two cars still outside the platform. I received a call from Line Controllor at 0823 hrs that a person has jumped in front of train 105 at Greenford. I informed Ian Williamson Train Operations Manager. We traveled on a special taxi with a spare Train Operator at 0839hrs and reached Greenford Station at 0859hrs. Emergency Services ( Police, London Ambulance, London Fire Brigade and ERU)

CREATE TABLE tbl_incd(
INCIDENT_NO NUMBER ,
SD_DESC VARCHAR2(4000 BYTE)
)
data for the above table
Insert into tbl_incd ( INCIDENT_NO, SD_DESC)
Values
(70000031,

'E105 on entering into platform by one cars lenght applied emergency brakes to stop the train due to a person under his train. Train stopped with two cars still outside the platform. I received a call from Line Controllor at 0823 hrs that a person has jumped in front of train 105 at Greenford. I informed Ian Williamson Train Operations Manager. We traveled on a special taxi with a spare Train Operator at 0839hrs and reached Greenford Station at 0859hrs. Emergency Services ( Police, London Ambulance, London Fire Brigade and ERU) were already on site. When spoken to Line Controlllor stated he received a normal radio call from E105 to inform him that he has got a person under his train. At 0826 Line Controllor had traction current switched off between Northolt and Greenford. Train service was suspended from North Acton to West Ruislip in both directions (east and west).

I could not speak to the Train Operator as Police was in the process of interviewing him and he was too traumatised to speak. Trauma Support was arranged from Loughton as we had no one available at West Ruislip and White City. Trauma Support spoke to T/OP over the telephone and Train Operator decided to travel in a special taxi which was booked for him on his own, although a Station Staff was was arranged to travel with him. During the process a spare T/OP stayed with this T/OP. When spoken to Mr. Clack Operations Security Manager stated he was traveling on this train from West Ruislip and made a telephone call to Network Operations Centre at 0826hrs to inform them of the situation. Mr. Clack travelled to the leading cab and confirmed that although the T/OP was badly shaken but he carried out his duties in a professinal manner by placing Short Circuiting Devise in front of the train and second SCD was placed on the rear of the track by Station Supervisor after traction current was discharged. Passengers were detrained by operation butterfly cock. Les Blaxwall Operations Standards Manager was also travelling on this train and offered his to T/OP. Mr. Blaxwall assisted in the wrong direction move and stayed till the end of the operation to assist. Wrong Direction move was carried out by T/OP Martin to assist emergency services for the track search. The deceased was an elderly of Asian origin approximately of 65yrs of age wearing white shirt, beige trauser and white trainers. When CCTV was viewed he was seen pacing up and down on the east bound platform near the waiting room. On approach of T105 he jumped in front of the train at 0824hrs and train stopped with two cars outside the station. The body was removed from platform at 0940hrs by ERU and taken in a body bag to the secure room at Greenford Station. Track was accessed by BTP to carry out track search for any trace of identification at 0932hrs and gave all clear at 0942hrs.

TOM Williamson assisted in closing the train doors by operating the butterfly cock to close position. Traction Current was switched on at 0948hrs and T105 was worked empty to North Acton and reversed to Ruislip Depot. All clear was given at 0951hrs and after station search, Greenford Station was re opened at 0955hrs. E142 was the first train to run in service on the east bound. Body was removed at 1013hrs from Greenford Station and taken to Uxbridge by the police. Trauma Support was offered to Station supervisor by his DSM, but he declined the offer. Service Manager and Line Controllor were kept informed by myself.');
Insert into tbl_incd ( INCIDENT_NO,SD_DESC)
Values

( 70000032'PART OF TRAIN WITHDRAWAL Train 17 had a 6 min delayed departure from White City due to the train having a defective speedometer. Train was changed over and dud train was sent to Ruislip Depot for the attention of the DDMs staff. Ruislip DDM confirmed that the speedometer was defective. This was traced to a defective ATP controller.');
Insert into tbl_incd ( INCIDENT_NO, SD_DESC)
Values

( 70000033,' had a 1 min delayed arrival at Ealing Broadway due to the train having problems at signal EAB2058. The T/op stated that the train was in ATO and was stopped at the red signal (2058). The signal cleared and the train moved forward, the signal went straight back to red and the train stopped. This happened once again. The train did not pass the signal. T/op contacted the Line controller via radio and the signal was cleared, with the train proceeding into the platform at Ealing Broadway. The train was taken to Hainault for the attention of the DDM and a download. Train download and Tracker net confirm the T/op`s account of events. Due to the serious implications of events, an investigation is being undertaken by the Duty Engineer at Wood Lane. The T/op carried out his duties in a professional and correct manner and informed the passengers of the situation as and when required.');
COMMIT;