Statement property maxRows incorrectly affects count(*) on table valued functions.

Setting statement property maxRows results in faulty row count on table valued functions. Below is the output from the supplied test program. The two functions numbers_tf and numbers_itf both return 10 rows. The former is table-valued function while the latter is an inlined version instead.

maxRows(0): select count(*) from dbo.numbers_itf() => 10  OK!
maxRows(5): select count(*) from dbo.numbers_itf() => 10  OK!
maxRows(0): select count(*) from dbo.numbers_tf() => 10  OK!
maxRows(5): select count(*) from dbo.numbers_tf() => 5  FAILED!

As can be seen setting maxRows to 5 changes the count to 5 instead of the expected 10. Clearly this is a bug. MaxRows should only affect the number of rows that the result set returns.

import java.math.BigInteger;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.concurrent.ThreadLocalRandom;

public class Main {
    public static void main(String[] args) throws SQLException {
        String url = "jdbc:sqlserver://localhost:1433";
        String user = "sa";
        String password = "Test1234!";
        String database = randomName("test_");
        try (
                Connection c = DriverManager.getConnection(url, user, password);
        ) {
            try {
                executeUpdate(c, "create database " + database);
                executeUpdate(c, "use " + database);


                executeUpdate(c, "create function dbo.numbers_itf()\n" +
                        "returns table\n" +
                        "as return\n" +
                        "    select * from (values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10)) t(num)\n" +
                        "\n");

                executeUpdate(c, "create function dbo.numbers_tf()\n" +
                        "  returns @result table (\n" +
                        "    num int\n" +
                        "  )\n" +
                        "  as\n" +
                        "  begin\n" +
                        "    insert into @result\n" +
                        "    select * from (values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10)) t(num)\n" +
                        "    return\n" +
                        "  end\n" +
                        "\n");


                executeTest(c, 0, "select count(*) from dbo.numbers_itf()", 10);
                executeTest(c, 5, "select count(*) from dbo.numbers_itf()", 10);
                executeTest(c, 0, "select count(*) from dbo.numbers_tf()", 10);
                executeTest(c, 5, "select count(*) from dbo.numbers_tf()", 10);

            } finally {
                executeUpdate(c,"use master");
                executeUpdate(c, "drop database " + database);
            }
        }
    }

    private static int executeUpdate(Connection c, String sql) throws SQLException {
        try (Statement s = c.createStatement()) {
            return s.executeUpdate(sql);
        }
    }

    private static void executeTest(Connection c, int maxRows, String sql, int expected) throws SQLException {
        try (Statement s = c.createStatement()) {
            s.setMaxRows(maxRows);
            s.execute(sql);
            try (ResultSet r = s.getResultSet()) {
                r.next();
                int actual = r.getInt(1);
                System.out.format("maxRows(%d): %s => %d  %s%n", s.getMaxRows(), sql, actual, (actual != expected ? "FAILED!" : "OK!"));
            }
        }
    }

    private static String randomName(String prefix) {
        return prefix + (new BigInteger(40, ThreadLocalRandom.current())).toString(32);
    }

}

[ulvii]

Instead of not reading the remaining packets after reaching maxRows, we could try to read and discard them. This might result in performance degradation when setMaxRows() is used, but also make the API JDBC compliant. I am currently looking into this, will try to create a PR as well as a few benchmarks.

[tseylerd]

@ulvii Good point. It’s the way how it should work (and how other jdbc drivers work). The point about the double parsing seems like an implementation detail. Why not parse it once and use the information to both count rows and create result set?