Statement.execute(sql) vs executeUpdate(sql) and executeQuery(sql)

I have a question related to this method: st.execute(sql); where st obviously is a Statement object. Directly from this oracle java tutorial:

execute: Returns true if the first object that the query returns is a ResultSet object. Use this method if the query could return one or more ResultSet objects. Retrieve the ResultSet objects returned from the query by repeatedly calling Statement.getResutSet.

What is meant by "one or more ResultSet objects"? How is it possible to manage them once got an array of ResultSet? Whereas st.executeQuery(sql) and st.executeUpdate(sql) are very clear. It's not (at least to me) the aim of st.execute(sql) which can also return an int as if it was updated a table.

Thanks in advance

Solution

What do they mean by "one or more ResultSet objects"?

The javadoc for the execute method says this:

"Executes the given SQL statement, which may return multiple results. In some (uncommon) situations, a single SQL statement may return multiple result sets and/or update counts. Normally you can ignore this unless you are (1) executing a stored procedure that you know may return multiple results or (2) you are dynamically executing an unknown SQL string."

That pretty much explains it. Sometimes a query can deliver more than one ResultSet.

if so how is it possible to manage them once got an array of ResultSet?

I'm not sure what you mean but:

you can't get them as an array: you must get them one at a time by calling getResultSet(), and
you could put the ResultSet objects into an array (if you knew how many to expect) or a List.

It's not (at least to me) the aim of st.execute(sql) which can also return an int as if it was updated a table.

One of the supported use-cases of execute mentioned in the quoted javadoc is to execute an unknown SQL statement. In this case, you don't know if it is a query, an update (of some kind) ... or something else that potentially delivers multiple result sets. This use-case requires the method to be able to return multiple results in some cases.

Basically, execute is a generalization of executeQuery() and executeUpdate(). If you don't need the generality, use the specialized versions instead.