Java SQL GROUP BY: Calculate Sum of Records Using SUM() Function

在Java中，可以使用SQL的GROUP BY子句结合SUM()函数来对返回的记录条数求和。以下是一个示例代码：\n\njava\nimport java.sql.*;\n\npublic class Main {\n public static void main(String[] args) {\n String url = "jdbc:mysql://localhost:3306/mydatabase";\n String username = "root";\n String password = "password";\n Connection conn = null;\n Statement stmt = null;\n ResultSet rs = null;\n\n try {\n conn = DriverManager.getConnection(url, username, password);\n stmt = conn.createStatement();\n\n String sql = "SELECT category, SUM(quantity) AS total FROM products GROUP BY category";\n rs = stmt.executeQuery(sql);\n\n while (rs.next()) {\n String category = rs.getString("category");\n int total = rs.getInt("total");\n System.out.println("Category: " + category + ", Total: " + total);\n }\n } catch (SQLException e) {\n e.printStackTrace();\n } finally {\n try {\n if (rs != null) {\n rs.close();\n }\n if (stmt != null) {\n stmt.close();\n }\n if (conn != null) {\n conn.close();\n }\n } catch (SQLException e) {\n e.printStackTrace();\n }\n }\n }\n}\n\n\n在上面的示例中，我们使用了MySQL数据库，并假设有一个名为products的表，其中包含category和quantity两个列。我们使用GROUP BY子句按category分组，并使用SUM()函数对quantity列求和。在循环中，我们从结果集中获取每个分组的category和求和后的total值，并打印出来。\n\n请注意，上述代码只是示例，实际应用中需要根据具体的数据库和表结构进行相应的修改。