我想在Java Eclipse中使用JDBC从上一个查询对ResultSet执行另一个SQL查询

Question

I have a JDBC project that I was just assigned in class and we are supposed to execute this query to our University database via JDBC Java Eclipse:

SELECT dept_name, COUNT(*) AS COUNT FROM student GROUP BY dept_name;

And with the returned resultSet query the result set with:

HAVING COUNT = (SELECT MAX(ACOUNT) AS MAXCOUNT
                FROM (SELECT dept_name, COUNT(*) AS ACOUNT
                      FROM student GROUP BY dept_name) AS ATable);

I have looked everywhere in my book and via google and can't find tutorials for examples on how to do this. Any links/documentation you guys can point me to or a starting point?

SOLUTION EDIT: I finally got clarification from my teacher, he meant to execute the SQL statement in my java program and loop through the results and using java and sift out the same information that the second SQL statement would acquire had it been attached to the original statement. Thank you to those that took the time to try and help.

Answer 1

Your assignment only provides pseudo-code, and the word "execute" must be a mistake. As advised by others, "executing a query on a result set" makes no sense.

Assuming your tutor meant "filter out" instead, you might be expected to run two separate statements ( SELECT dept_name... and SELECT MAX(... ), then iterate over the first result set searching for the result that matches the second result set.

Pseudo-code:

RSet1 = query("SELECT dept_name, COUNT(*) AS COUNT FROM student GROUP BY dept_name;");
RSet2 = query("SELECT MAX(ACOUNT) AS MAXCOUNT ...");
RowInR2 = RSet2[0]; // first and only row

foreach RowInR1 in RSet1
    if (
        RowInR1.count = RowInR2.maxcount
    ) {
        return RowInR1; // this is your result
    }
}

Please bear in mind this approach is absurd except for education purpose. It is possible to extract this data (one single row) in just one query, without the need to extract and parse the results from [Query 1] (this query is the exact concatenation of your two queries).