Query 2 : select top 1 1 from syscolumns,syscolumns where 1=1

QUERY 2 : Error ambigus col name

Query 2 : select top 1 1 from syscolumns,syscolumns where 1=1

Query 2 : select top 1 1 from syscolumns,syscolumns where 1=1 Ambiguous col. name?

Query 2 : select top 1 1 from syscolumns,syscolumns where 1=1

Nice question.

Answer is query 2. Same table name used two times so need to use alias in one of the table name.

The correct answer is that query #2 will produce an Ambiguous column name error. The reason is simple - the column #1 for both queries would have the same name and come from the same table, resulting in SQL Server to be confused on what it should pick.

The good thing about trying to answer questions without executing the queries in them is that it forces you to think about what's going on under the hood. So, keep them coming!

Option 2

Query 2 throws error.If we need to use a table more than once in a query, need to use alias name.