How to Fix SQL Ambiguous Column Error

In SQL, ambiguous column error you can see many times. Here’re a few examples of how to resolve this error. Here is a link for SQL set operators 10 Top Rules for SQL Set Operators.

What is Ambiguous Column Error

The ambiguous columns mean, SQL does not understand which column it has to consider.

Let me explain in detail. In the classroom, there are two boys with the same name…

Okay.

If a teacher calls the name, both boys look up their heads. So, it is confusing to the teacher and the classroom…..students who are sitting inside.

So, the teacher made some changes…

Added some uniqueness to each boy’s name…

Then, the problem is resolved.

How to Resolve Ambiguous column error?

The fix or resolution for the ambiguous column is as follows:

SELECT invoice_numb, 
       vendor_name 
FROM   vendors 
       INNER JOIN invoices 
               ON vendor_id = vendor_id 
ORDER  BY invoice_numb;  

In the above query, the incorrectness is you are joining on vendor_id. The problem is vendor_id is present in both the tables. This is called ambiguous.

 SELECT invoice_numb, 
       vendor_name 
FROM   vendors 
       INNER JOIN invoices 
               ON vendors.vendor_id = invoices.vendor_id 
ORDER  BY invoice_numb;  

According to BURLESON, A column name used in a join exists in more than one table and is thus referenced ambiguously.

How I fixed?

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. Read his example here.

According to Oracle documents.

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.

Also read,

32 Tricky SQL queries you need for all interviews

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