ORA-00918: column ambiguously defined

ORA-00918: column ambiguously defined

Cause :A column name used in a join exists in more than one table and is thus referenced ambiguously. In a join, any column name that occurs in more than one of the tables must be prefixed by its table name when referenced. The column should be referenced as TABLE.COLUMN or TABLE_ALIAS.COLUMN. For example, if tables EMP and DEPT are being joined and both contain the column DEPTNO, then all references to DEPTNO should be prefixed with the table name, as in EMP.DEPTNO or E.DEPTNO.

Action: Prefix references to column names that exist in multiple tables with either the table name or a table alias and a period (.), as in the examples above.

When ORA-00918 is thrown, you have a column which has been ambiguously defined.  If a column name in a join is referenced ambiguously, it exists in multiple tables.
-- Column names which occur in multiple tables should be prefixed when it is referenced by its table name.
-- Columns must be referenced as TABLE.COLUMN or TABLE_ALIAS.COLUM .  Oracle documentation which reference ORA-00918 give the following example:
-- If tables EMP and DEPT are being joined and both contain the column DEPTNO, then all references to DEPTNO should be prefixed with the table name, as in EMP.DEPTNO or E.DEPTNO.

To correct ORA-00918, references should be prefixed to column names existing in multiple tables (either with the table name or table alias and a period)