（六）MySQL自定義函數應用場景

先記應用示例：

自定義函數 (user-defined function UDF)就是用一個象ABS() 或 CONCAT()這樣的固有（內建）函數一樣作用的新函數去擴展MySQL。

所以UDF是對MySQL功能的一個擴展

個人實踐中，高度抽象的查詢邏輯，可以寫成MySQL函數。之前在項目中，查詢客戶的推薦人，遞歸到頂級。查詢客戶的下級樹，遞歸層數有30多層。在程序中寫遞歸查詢，效率很低，控制台飄着的全是SQL，借鑒他人的做法，把遞歸的邏輯寫在了DB層，很好的提高了效率。

函數調試：

本人是建了張表，臨時變量存進去，判斷執行過程的，暫未掌握函數DEBUG方法

通用的樹操作示例：

建表：

CREATE TABLE IF NOT EXISTS t_user( 
    id INT(11) AUTO_INCREMENT PRIMARY KEY, 
    `level` INT(11) DEFAULT 1,
    parent_id INT(11) DEFAULT 0,
    `name` VARCHAR(20),
    `age` TINYINT(11) UNSIGNED,
    `gender` TINYINT(11) UNSIGNED DEFAULT 0 COMMENT '0:男；1:女'
) ENGINE = InnoDB COMMENT = '用戶信息表';

初始化數據：

INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 0, '張三', 14, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 0, '李四', 12, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(2, 1, '王五', 13, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(2, 2, '趙六', 45, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(3, 3, '簡柒', 34, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(3, 4, '王八', 23, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(3, 4, '何九', 12, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(4, 5, '石十', 98, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(4, 5, '范十一', 87, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(4, 6, '夏十二', 76, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(4, 7, '湯十三', 65, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 7, '彭十四', 54, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 5, '楊十五', 43, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 6, '鐵十六', 32, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 7, '郭十七', 32, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 8, '牛十八', 21, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 9, '蔡十九', 79, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 9, '白二十', 57, 0);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 8, '朱二一', 46, 1);
INSERT INTO t_user(`level`, `parent_id`, name, age, gender) VALUES(1, 10, '林二二', 35, 0);

遞歸到頂級的函數：

DROP FUNCTION IF EXISTS getParentsUser;
CREATE FUNCTION `getParentsUser`(rootId INT)
RETURNS varchar(1000) 
BEGIN
    DECLARE sTemp VARCHAR(1000);
    DECLARE sTempPar VARCHAR(1000); 
    SET sTemp = ''; 
    SET sTempPar =rootId; 
 
    -- 循環遞歸
    WHILE sTempPar is not null DO 
        -- 判斷是否是第一個，不加的話第一個會為空
        IF sTemp != '' THEN
            SET sTemp = concat(sTemp,',',sTempPar);
        ELSE
            SET sTemp = sTempPar;
        END IF;
        SET sTemp = concat(sTemp,',',sTempPar); 
        SELECT group_concat(pid) INTO sTempPar FROM treenodes where pid<>id and FIND_IN_SET(id,sTempPar)>0; 
    END WHILE; 
 
RETURN sTemp; 
END

遞歸子節點的函數：

DROP FUNCTION IF EXISTS findChildrenUser;
CREATE FUNCTION findChildrenUser(rootId INT)
RETURNS VARCHAR(4000)
BEGIN
DECLARE sTemp VARCHAR(4000);
DECLARE sTempChd VARCHAR(4000);

SET sTemp='$';
SET sTempChd = CAST(rootId AS CHAR);

WHILE sTempChd IS NOT NULL DO
SET sTemp= CONCAT(sTemp,',',sTempChd);
SELECT GROUP_CONCAT(id) INTO sTempChd FROM t_user WHERE FIND_IN_SET(parent_id,sTempChd)>0;
END WHILE;
RETURN sTemp;
END;

查詢：

mysql> SELECT getParentsUser(15);
+-----------------------+
| getParentsUser(15)    |
+-----------------------+
| 15,15,7,7,4,4,2,2,0,0 |
+-----------------------+
1 row in set (0.00 sec)

mysql> SELECT getChildrenUser(2);
+-----------------------------+
| getChildrenUser(2)          |
+-----------------------------+
| $,2,4,6,7,10,11,12,14,15,20 |
+-----------------------------+
1 row in set (0.00 sec)

組合使用：

測試以下查詢效率很低，暫不清楚原因，項目中選擇了分部查。先查id集合，再用in查行記錄

mysql> SELECT * FROM t_user WHERE FIND_IN_SET(id, getParentsUser(15));
+----+-------+-----------+-----------+------+--------+
| id | level | parent_id | name      | age  | gender |
+----+-------+-----------+-----------+------+--------+
|  2 |     1 |         0 | 李四      |   12 |      1 |
|  4 |     2 |         2 | 趙六      |   45 |      0 |
|  7 |     3 |         4 | 何九      |   12 |      1 |
| 15 |     4 |         7 | 郭十七    |   32 |      1 |
+----+-------+-----------+-----------+------+--------+
4 rows in set (0.02 sec)

mysql> SELECT * FROM t_user WHERE FIND_IN_SET(id, getChildrenUser(2));
+----+-------+-----------+-----------+------+--------+
| id | level | parent_id | name      | age  | gender |
+----+-------+-----------+-----------+------+--------+
|  2 |     1 |         0 | 李四      |   12 |      1 |
|  4 |     2 |         2 | 趙六      |   45 |      0 |
|  6 |     3 |         4 | 王八      |   23 |      0 |
|  7 |     3 |         4 | 何九      |   12 |      1 |
| 10 |     4 |         6 | 夏十二    |   76 |      1 |
| 11 |     4 |         7 | 湯十三    |   65 |      0 |
| 12 |     4 |         7 | 彭十四    |   54 |      1 |
| 14 |     4 |         6 | 鐵十六    |   32 |      0 |
| 15 |     4 |         7 | 郭十七    |   32 |      1 |
| 20 |     5 |        10 | 林二二    |   35 |      0 |
+----+-------+-----------+-----------+------+--------+
10 rows in set (0.02 sec)

隨機數

方便后續測試SQL效率，索引優化，寫批量插入腳本

獲取隨機字符串：

DELIMITER //
CREATE FUNCTION RANDOM_STR(length int) 
RETURNS VARCHAR(255)
BEGIN
DECLARE meta_str VARCHAR(62) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
DECLARE target_str VARCHAR(255) default '';
DECLARE i INT DEFAULT 0;
WHILE i < length DO
	SET target_str = CONCAT(target_str, SUBSTRING(meta_str,FLOOR(1 + RAND() * 62), 1));
	SET i = i + 1;
END WHILE;
RETURN target_str;
END //

測試：

mysql> SELECT RANDOM_STR(5);
+---------------+
| RANDOM_STR(5) |
+---------------+
| omuds         |
+---------------+
1 row in set (0.00 sec)

mysql> SELECT RANDOM_STR(5);
+---------------+
| RANDOM_STR(5) |
+---------------+
| uTRrr         |
+---------------+
1 row in set (0.00 sec)

mysql> SELECT RANDOM_STR(7);
+---------------+
| RANDOM_STR(7) |
+---------------+
| Li6kg9I       |
+---------------+
1 row in set (0.00 sec)

獲取隨機整數值：

DELIMITER //
CREATE FUNCTION RANDOM_NUMBER(min INT, max INT) 
RETURNS INT
BEGIN
DECLARE target_no INT;
SELECT FLOOR(RAMD() * (max - min) + min) INTO target_no;
RETURN target_no;
END //

測試：

mysql> SELECT RANDOM_NUMBER(3,5);
+--------------------+
| RANDOM_NUMBER(3,5) |
+--------------------+
|                  3 |
+--------------------+
1 row in set (0.00 sec)

mysql> SELECT RANDOM_NUMBER(3,5);
+--------------------+
| RANDOM_NUMBER(3,5) |
+--------------------+
|                  4 |
+--------------------+
1 row in set (0.00 sec)

mysql> SELECT RANDOM_NUMBER(3,5);
+--------------------+
| RANDOM_NUMBER(3,5) |
+--------------------+
|                  3 |
+--------------------+
1 row in set (0.00 sec)

mysql> SELECT RANDOM_NUMBER(3,5);
+--------------------+
| RANDOM_NUMBER(3,5) |
+--------------------+
|                  4 |
+--------------------+
1 row in set (0.00 sec)

mysql> SELECT RANDOM_NUMBER(3,5);
+--------------------+
| RANDOM_NUMBER(3,5) |
+--------------------+
|                  4 |
+--------------------+
1 row in set (0.00 sec)