CREATE TABLE failed ORA 00957 Duplicate column name - sql

Question

As I tried to create new table from existing 2 table with specific column name in oracle.
I tried below code
CREATE TABLE D_T1
AS
SELECT a.col1, a.col2, a.col3, a.col4, a.col5, b.col6, b.col7, b.col8
FROM db1.table1 a INNER JOIN db1.table2 b
ON (a.col1 = b.colNum AND a.col2 = b.colnum1)
But I get error
CREATE TABLE failed ORA 00957 Duplicate column name
Can anyone help?

Answer 1

Ignoring the other errors you seem to have introduced by retyping the code, you've shown that you do have a duplicate column, which is what the error is telling you:
a.VALIDFLAG, b.VALIDFLAG
You seem to be under the impression that the table (alias) prefix makes the column names in the projection unique. They do not. The table prefix tells Oracle which table to get the column value from (unless you're using the using join syntax, which you are not). If the column appears in two tables you have to prefix the column name with the table. If you want the value from both tables you have to prefix both of them.
With a simple query then referring to both table columns without column aliases is OK, but something trying to consume the result set might struggle. This is fine:
select a.dummy, b.dummy
from dual a
join dual b on b.dummy = a.dummy;
DUMMY DUMMY
------- -------
X X
But notice that both columns have the same heading. If you tried to create a table using that query:
create table x as
select a.dummy, b.dummy
from dual a
join dual b on b.dummy = a.dummy;
You'd get the error you see, ORA-00957: duplicate column name.
If you alias the duplicated columns then the problem goes away:
create table x as
select a.dummy as dummy_a, b.dummy as dummy_b
from dual a
join dual b on b.dummy = a.dummy;
So in your case you can alias those columns, if you need both:
..., a.VALIDFLAG AS validflag_a, b.VALIDFLAG AS validflag_b, ...

Answer 2

To be completely honest, that query is a mess. You've got several errors in your SQL statement:
CREATE TABLE AS SELECT
The table name is missing - this should be
CREATE TABLE my_new_table AS SELECT
to create a new table named my_new_table.
a.ALIDFLAG,b,VALIDFLAG,
I've got a suspicion that this should really be a.VALIDFLAG instead of a.ALIDFLAG. Also, you need to replace b,VALIDFLAG with b.VALIDFLAG.
SELECT a.BILLFREQ a.CDHRNUM,
You're missing a comma after a.BILLFREQ - this is a syntax error.
a.A‌​GNYCOY,a.AGNTCOY
There's the culprit - you're selecting the same column twice. Get rid of the second one.
EDIT Actually, the names are different, so this isn't the cause of the error (unless you've mistyped your query in the comment instead of copy& paste).
To debug this kind of errors, try to
format your SQL statement in a readable way
comment out everything but one column, run the statement and ensure it works
add one column
repeat until you find the error or you've added all columns
2ND UPDATE
With the updated query, the error is here:
a.VALIDFLAG,
b,
VALIDFLAG,
You have two columns named VALIDFLAG - use an alias for one of these, and it should work.

Answer 3

ORA-00957: duplicate column name
The only reason for that error in your CTAS statement is that you have similar column name in the SELECT statement. Though you might be referring to different table columns, but you did not use a column alias
Error reproduce:
Using the standard EMP and DEPT table.
SQL> CREATE TABLE D_T1 AS
2 SELECT a.deptno,
3 b.deptno
4 FROM emp A
5 INNER JOIN dept b
6 ON (a.deptno = b.deptno);
b.deptno
*
ERROR at line 3:
ORA-00957: duplicate column name
Workaround:
Use proper alias:
SQL> CREATE TABLE D_T1 AS
2 SELECT a.deptno e_deptno, --add column alias
3 b.deptno d_deptno --add column alias
4 FROM emp a
5 INNER JOIN dept b
6 ON (a.deptno = b.deptno);
Table created.

Answer 4

Edit as per new input from OP.
You have some syntax error in your query. Corrected those. I also checked for duplicate columns. There are none. Now run this and let me know if you still get same error.
CREATE TABLE D_T1 AS SELECT
a.B, a.C,a.C, a.C, a.C,a.J, a.O,
a.P,a.P,a.S,a.S,a.R,a.B,
a.S,a.S,b.A,b.C,b.C,b.I, b.M,
b.P,b.P,b.S,b.S,b.S,b.Z,b.Z,a.C,
a.CH‌​,a.G,b,V,b.T,a.C,a.C,a.C,
a.A,a.A‌​Ga.AG
FROM tbl1 a JOIN tbl2 b
ON (a.C= b.C AND a.C1= b.C1)