Determining Presence or Absence of a Result Set

9.4.1 Problem

You just executed a query obtained from an external source, so you're not sure whether it returned a result set.

9.4.2 Solution

Check the column count in the metadata. If the count is zero, there is no result set.

9.4.3 Discussion

If you write an application that accepts query strings from an external source such as a file or a user entering text at the keyboard, you may not necessarily know whether or not any given query returns a result set. That's an important distinction, because queries that return a result set are processed differently than those that do not. One way to tell the difference is to check the metadata value that indicates the column count after executing the query. Assuming that no error occurred, a column count of zero indicates that the query was an INSERT, UPDATE, or other statement that returns no result set. A nonzero value indicates the presence of a result set and you can go ahead and fetch the rows. This technique works to distinguish SELECT from non-SELECT queries, even for SELECT queries that return an empty result set. (An empty result is different than no result. The former returns no rows, but the column count is still correct; the latter has no columns at all.)

Some APIs provide other ways to distinguish query types than checking the column count. In JDBC, you can issue arbitrary queries using the execute( ) method, which directly indicates whether there is a result set by returning true or false. In Python, the value of cursor.description is None for statements that produce no result set.