Have you ever encountered the error message “ORA-00918 Column Ambiguously Defined” when executing a SQL statement in Oracle Database?
If so, you are not alone. This error message is a common problem among Oracle users and can be caused by several reasons.
In this article, we will dive deep into what “ORA-00918 Column Ambiguously Defined” means, why it occurs, and how to resolve it effectively.
What is ORA-00918 Column Ambiguously Defined?
ORA-00918 is an error message that appears when a column name in a SQL statement is used without specifying the table it belongs to, resulting in ambiguity. This error message means that Oracle cannot determine which table the column belongs to, thus preventing the statement from executing.
For example, the following SQL statement would result in an ORA-00918 error:
SELECT column1, column2
FROM table1, table2;
In this case, Oracle would not know which “column1” and “column2” belong to. To resolve this issue, the column names need to be fully qualified with the table names, like so:
SELECT table1.column1, table2.column2
FROM table1, table2;
Causes of ORA-00918 Column Ambiguously Defined
The ORA-00918 error can be caused by several reasons, including:
- Joining two tables with the same column name
- Selecting columns from multiple tables with the same name
- Using an alias for a table that results in a column name collision
- Using a synonym that points to a column with the same name in multiple tables
How to resolve ORA-00918 Column Ambiguously Defined
To resolve the ORA-00918 error, you need to fully qualify the column names with the table names. This can be done by:
- Using table aliases
- Using the table name followed by a dot (.) before the column name
For example, if you have two tables with the same column name, you can use table aliases to differentiate between them, like so:
SELECT t1.column1, t2.column1
FROM table1 t1, table2 t2;
If you are using a synonym that points to a column with the same name in multiple tables, you can fully qualify the column name with the table name, like so:
SELECT table1.column1
FROM table1;
Conclusion
In conclusion, encountering the “ORA-00918 Column Ambiguously Defined” error is a common problem among Oracle users. It can be caused by several reasons, including joining two tables with the same column name, selecting columns from multiple tables with the same name, using an alias for a table that results in a column name collision, and using a synonym that points to a column with the same name in multiple tables. To resolve the error, you need to fully qualify the column names with the table names, either by using table aliases or by using the table name followed by a dot (.) before the column name.
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