-- 會員表單
CREATE TABLE IF NOT EXISTS tbl_member (
	m_id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
	m_name VARCHAR(100) COMMENT '會員姓名',
	parent_id INT UNSIGNED DEFAULT 0 COMMENT '上線 ID'
) ENGINE=MYISAM COLLATE utf8_unicode_ci CHARACTER SET utf8;

-- a 為最大上線
-- b 以及 c 為 a 的下線
-- d 為 b 的下線
-- e 為 c 的下線
INSERT INTO tbl_member (m_name, parent_id) VALUES('a', 0);
INSERT INTO tbl_member (m_name, parent_id) VALUES('b', 1);
INSERT INTO tbl_member (m_name, parent_id) VALUES('c', 1);
INSERT INTO tbl_member (m_name, parent_id) VALUES('d', 2);
INSERT INTO tbl_member (m_name, parent_id) VALUES('e', 3);

-- 金額紀錄
CREATE TABLE IF NOT EXISTS tbl_sale (
	s_id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
	m_id INT UNSIGNED DEFAULT 0 COMMENT '會員 ID',
	s_money INT UNSIGNED DEFAULT 0 COMMENT '金額',
	s_date DATETIME COMMENT '日期紀錄',
	parent_id INT UNSIGNED DEFAULT 0 COMMENT '上線 ID'
) ENGINE=MYISAM COLLATE utf8_unicode_ci CHARACTER SET utf8;

INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (2, 100, NOW(), 1);
INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (2, 200, NOW(), 1);
INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (3, 300, NOW(), 1);
INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (3, 400, NOW(), 1);
INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (4, 100, NOW(), 2);
INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (4, 200, NOW(), 2);
INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (5, 200, NOW(), 3);
INSERT INTO tbl_sale (m_id, s_money, s_date, parent_id) VALUES (5, 300, NOW(), 3);

下線無窮延伸的直銷系統
假設以 a 為第一層，應該要抓出 b、c、d、e 的金額總和
不知道怎麼寫比較有效率