Mysql-Explain（二）：explain實驗數據準備

上一篇博客簡單介紹了explain的作用，並且通過表格的形式羅列出了所有explain輸出列的相關信息。不過如果僅僅看文字可能還是難以理解其中的含義，更何況本人文筆羞澀，還可能會存在言不達意的情況，所以還是通過實驗來一一解讀較好。

實驗所需要的表格一共有三張：student、school、major，表結構如下

• stuednt：學生
  
• school：學校
  
• major：專業
  

通過sql腳本來創建表和插入實驗數據

• Sql腳本執行之前先修改log_bin_trust_function_creators的值，這是因爲腳本包含函數和過程的創建。

  mysql> show variables like "log_bin_trust_function_creators";
  +---------------------------------+-------+
  | Variable_name                   | Value |
  +---------------------------------+-------+
  | log_bin_trust_function_creators | OFF   |
  +---------------------------------+-------+
  1 row in set, 1 warning (0.00 sec)
  

  如果是OFF或者0，則需要通過下面的語句修改，等後面的sql腳本執行完後，可以再考慮修改回原來的值。

  -- -----------
  -- 0=OFF  1=ON
  -- -----------
  set global log_bin_trust_function_creators = 1;
  

• 導入sql腳本

  -- ----------------------------
  -- 整個過程執行可能要幾分鐘的時間
  -- ----------------------------
  SET NAMES utf8mb4;
  SET FOREIGN_KEY_CHECKS = 0;
  
  -- ----------------------------
  -- Table structure for major
  -- ----------------------------
  DROP TABLE IF EXISTS `major`;
  CREATE TABLE `major`  (
    `id` int(11) NOT NULL,
    `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
    PRIMARY KEY (`id`) USING BTREE
  ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;
  
  -- ----------------------------
  -- Table structure for school
  -- ----------------------------
  DROP TABLE IF EXISTS `school`;
  CREATE TABLE `school`  (
    `id` int(11) NOT NULL,
    `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
    PRIMARY KEY (`id`) USING BTREE
  ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;
  
  -- ----------------------------
  -- Table structure for student
  -- ----------------------------
  DROP TABLE IF EXISTS `student`;
  CREATE TABLE `student`  (
    `id` int(11) NOT NULL,
    `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
    `age` int(11) NULL DEFAULT NULL,
    `school_id` int(11) NULL DEFAULT NULL,
    `major_id` int(11) NULL DEFAULT NULL,
    PRIMARY KEY (`id`) USING BTREE
  ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;
  
  -- ----------------------------
  -- Procedure structure for insert_majors
  -- ----------------------------
  DROP PROCEDURE IF EXISTS `insert_majors`;
  delimiter ;;
  CREATE PROCEDURE `insert_majors`(num int)
  BEGIN
  	DECLARE i INT DEFAULT 0;
  	DECLARE EXIT HANDLER FOR SQLEXCEPTION BEGIN ROLLBACK; SELECT -1; END;
  	START TRANSACTION;
  	REPEAT
  		SET i = i + 1;
  		INSERT INTO major VALUES(i,CONCAT('專業',i));
  	UNTIL i = num END REPEAT;
  	COMMIT;
  END
  ;;
  delimiter ;
  
  -- ----------------------------
  -- Procedure structure for insert_schools
  -- ----------------------------
  DROP PROCEDURE IF EXISTS `insert_schools`;
  delimiter ;;
  CREATE PROCEDURE `insert_schools`(num int)
  BEGIN
  	DECLARE i INT DEFAULT 0;
  	DECLARE EXIT HANDLER FOR SQLEXCEPTION BEGIN ROLLBACK; SELECT -1; END;
  	START TRANSACTION;
  	REPEAT
  		SET i = i + 1;
  		INSERT INTO school VALUES(i,CONCAT('學校',i));
  	UNTIL i = num END REPEAT;
  	COMMIT;
  END
  ;;
  delimiter ;
  
  -- ----------------------------
  -- Procedure structure for insert_students
  -- ----------------------------
  DROP PROCEDURE IF EXISTS `insert_students`;
  delimiter ;;
  CREATE PROCEDURE `insert_students`(start int,num int)
  BEGIN
  DECLARE i INT DEFAULT 0;
  DECLARE EXIT HANDLER FOR SQLEXCEPTION BEGIN ROLLBACK; SELECT -1; END;
   
    START TRANSACTION;
  	REPEAT
  	set i = i + 1;
  	insert into student values(start + i,rand_str(10),FLOOR(20 + RAND() * 10),FLOOR(RAND() * 1000),FLOOR(RAND() * 500));
    UNTIL i = num END REPEAT;
  	COMMIT;
  	SELECT 1;
   END
  ;;
  delimiter ;
  
  DROP PROCEDURE IF EXISTS `insert_students2`;
  delimiter ;;
  CREATE PROCEDURE `insert_students2`(batch int,num int)
  BEGIN
  DECLARE i INT DEFAULT 0;
  DECLARE EXIT HANDLER FOR SQLEXCEPTION BEGIN SELECT i; END;
   
    START TRANSACTION;
  	REPEAT
  	set i = i + 1;
  	call insert_students((i-1) * num ,num);
    UNTIL i = batch END REPEAT;
  	COMMIT;
  	SELECT i;
   END
  ;;
  delimiter ;
  
  -- ----------------------------
  -- Function structure for rand_str
  -- ----------------------------
  DROP FUNCTION IF EXISTS `rand_str`;
  delimiter ;;
  CREATE FUNCTION `rand_str`(n int)
   RETURNS varchar(255) CHARSET utf8mb4 COLLATE utf8mb4_general_ci
  BEGIN
  	DECLARE char_str VARCHAR(100) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
  	DECLARE return_str VARCHAR(255) DEFAULT '';
  	DECLARE i INT DEFAULT 0;
  	WHILE i < n DO
  		SET return_str = CONCAT(return_str,SUBSTRING(char_str,FLOOR(1+RAND() * 52),1));
  		SET i = i + 1;
  	END WHILE;
  	RETURN return_str;
  END
  ;;
  delimiter ;
  
  -- 如果要改變插入表的數據行數，可以修改這裏的參數
  call insert_schools(1000);
  call insert_majors(500);
  -- 第一個參數分20批次插入，第二個參數每個批次插入100000，所以一共是200w條記錄
  call insert_students2(20,100000);
  
  SET FOREIGN_KEY_CHECKS = 1;
  

檢查表和數據

• student：一共插入了200w行記錄，由於是實驗數據所以學生名稱是隨機生成的字符串
  
• school：一共插入1000行記錄
  
  
• major：一共插入500行記錄
  
  

三張表暫時都還不創建索引，這等到後續實驗的時候再陸續創建。

有了實驗的表和數據後，那就可以執行後面的實驗啦。