Database Reference
In-Depth Information
10.3. Determining Whether a Statement Produced a
Result Set
Problem
You just executed an SQL statement, but you're not sure whether it produced a result
set.
Solution
Check the column count in the metadata. There is no result set if the count is zero.
Discussion
If you write an application that accepts statement strings from an external source such
as a file or a user entering text at the keyboard, you may not necessarily know whether
it's a statement such as
SELECT
that produces a result set or a statement such as
UP
DATE
that does not. That's an important distinction because you process statements that
produce a result set differently from those that do not. Assuming that no error occurred,
one way to tell the difference is to check the metadata value that indicates the column
count after executing the statement (as shown in
Recipe 10.2
). A column count of zero
indicates that the statement was an
INSERT
,
UPDATE
, or some 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 distinguishes
SELECT
from non-
SELECT
statements,
even for
SELECT
statements that return an empty result set. (An empty result is different
from no result. The former returns no rows, but the column count is still correct; the
latter has no columns at all.)
Some APIs provide ways to distinguish statement types other than checking the column
count:
• In Python, the value of
cursor.description
is
None
for statements that produce
no result set.
• In JDBC, you can issue arbitrary statements using the
execute()
method, which
returns true or false to indicate whether there is a result set.
10.4. Using Metadata to Format Query Output
Problem
You want to display a result set, nicely formatted.
