java - 如何从 ResultSet 对象中获取 COUNT？

Question

我将以下查询传递给 ResultSet 对象：

String query = "SELECT COUNT( DISTINCT KEY ), SOURCE FROM MY_TBL\n" +
            "GROUP BY SOURCE\n" +
            "ORDER BY SOURCE";

我想捕获我为每个 SOURCE 获得的计数并将它们加总。我如何通过 ResultSet 捕获这些计数，因为 COUNT 不是 ResultSet 中的列名，我认为我不能通过返回它的值rs.getInt("COUNT")？

Answer 1

getInt重载，使用索引（an ）而不是int列名：

 rs.getInt(1); // the first column is 1

Answer 2

尝试使用别名

String query = "SELECT COUNT( DISTINCT KEY ) AS COUNT, SOURCE FROM MY_TBL\n" +
        "GROUP BY SOURCE\n" +
        "ORDER BY SOURCE";

Answer 3

我认为最好使用

Statement st = conn.createStatement();
ResultSet rs = st.executeQuery("SELECT * from Customer");
ResultSetMetaData rsmd = rs.getMetaData();

int numCols = rsmd.getColumnCount();

Answer 4

我认为“getColumnCount”重新定义表中的列数而不是行数......