How to insert from one table to another (multiple columns to single column)

Question

I want to insert data from table1 into table2 and the data looks in 3 columns as below
Table1     
RepNm ObjNm DbNm
123     abc def
456     def xyz
789     123 456
and the data in table2 should be display as
Table 2
ObjNm
123
456
789
abc
def
xyz
the dupes should get eliminated and only the distinct values should be inserted into a single column in table2 from multiple columns in table1

Answer 1

How do you want to handle nulls? If there is a null in any value of a column, do you want to insert it?
Then,
WITH T
     AS (SELECT LEVEL colnum
           FROM DUAL
         CONNECT BY LEVEL <= 3)
SELECT DECODE (colnum,  1, RepNm,  2, ObjNm,  3, DbNm) as ObjNm
  FROM table1, T;if you dont want to insert nulls then,
WITH T
     AS (SELECT LEVEL colnum
           FROM DUAL
         CONNECT BY LEVEL <= 3)
SELECT DECODE (colnum,  1, RepNm,  2, ObjNm,  3, DbNm) AS ObjNm
  FROM table1, T
WHERE DECODE (colnum,  1, RepNm,  2, ObjNm,  3, DbNm) = DECODE (colnum,  1, RepNm,  2, ObjNm,  3, DbNm)G.