CREATE TABLE t1(f1 int , f3 int);
CREATE TABLE t2(f1 int , f3 int);
CREATE VIEW v1
as
SELECT
t1.f1, -- please note the column name will be f1 in v1
t2.f1, -- please note the column name will be f1 in v1
t1.f2, t2.f3
FROM t1, t2
WHERE t1.f1 = t2.f1;
If you executed the above SQL against Oracle database, there will be a ORA-00957 error which means duplicate column name.
But the following SQL query will be executed succefully, because the view column name is specified.
CREATE VIEW v1 (t1f1, t2f1, t1f2, t2f3)
as
SELECT
t1.f1,
t2.f1,
t1.f2, t2.f3
FROM t1, t2
WHERE t1.f1 = t2.f1;