Ambiguous column name error

Question

When executing the following (complete) SQL query on Microsoft SQL Server 2000:

SELECT B.ARTIFACTTNS, B.ARTIFACTNAME, B.ARTIFACTTYPE, B.INITIALBYTES, B.TIMES         


        

Answer 1

Because ARTIFACTTYPE can refer to either A.ARTIFACTTYPE or B.ARTIFACTTYPE and the server needs to know which one you want, just change it to A.ARTIFACTTYPE and you should be okay in this case.

To clarify, you need to specify the alias prefix any time the column name is ambiguous. It isn't bad practice to always use alias prefixes as it makes it clear which columns are coming from which tables when you read the query, and eliminates issues like this one.

One might wonder why you need to distinguish between which of two columns you want when they both refer to the same column in the same table. The answer is that when you join a table to itself, the values from A.column and B.column may be different depending on the join criteria (such as may be the case with an outer join where values in one of the columns may be null).