Mysql Limit 调优

Posted 2021-02-15 tanoak

1. 建表与插入数据
2. SQL对比

基本数据

• 创建表

  CREATE TABLE student
  (
    id  int(10) NOT NULL AUTO_INCREMENT,
    name varchar(25) DEFAULT NULL,
    age tinyint(2) DEFAULT NULL,
    live varchar(255) DEFAULT NULL,
    PRIMARY KEY (id)
  ) ;

• 批量插入1百万条数据

DROP PROCEDURE IF EXISTS insert_Stu;
DELIMITER $$
CREATE PROCEDURE insert_Stu(IN max_num INT(10))
BEGIN
  DECLARE i INT DEFAULT 0;
  REPEAT
    SET i = i + 1;
    INSERT INTO student (name, age, live) VALUES (rand_string(3), rand_num(), rand_string(6));
  UNTIL i = max_num
    END REPEAT;
  COMMIT;
END $$

DROP PROCEDURE IF EXISTS rand_string;
DELIMITER $$
CREATE FUNCTION rand_string(n INT) RETURNS VARCHAR(255)
BEGIN
  DECLARE chars_str VARCHAR(100) DEFAULT 'abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ';
  DECLARE return_str VARCHAR(255) DEFAULT '';
  DECLARE i INT DEFAULT 0;
  WHILE i < n DO
  SET return_str = CONCAT(return_str, SUBSTRING(chars_str, FLOOR(1 + RAND() * 52), 1));
  SET i = i + 1;
  END WHILE;
  RETURN return_str;
END $$;

DROP PROCEDURE IF EXISTS rand_num;
DELIMITER $$
CREATE FUNCTION rand_num()
  RETURNS INT(5)
BEGIN
  DECLARE i INT DEFAULT 0;
  SET i = FLOOR(100 + RAND() * 10);
  RETURN i;
END $$
;

call insert_Stu(1000000);

SQL对比

1. 常规分页

   select s.* from student s limit 1000000,10;

2. 优化分页

   select s.*
   from student s
   WHERE s.id >= (SELECT s.id FROM student LIMIT 1000000, 1)
   LIMIT 10;

3. 最优分页

   SELECT s.* FROM student s WHERE s.id BETWEEN 1000000 AND 1000010;

4. 性能对比图

   可以看到三种SQL的耗时 ，为什么会有这么大的差距，这主要是mysql的limit关键字会导致偏移量的原因