Mysql Limit 调优

tanoak

发布于 2019-04-18 16:44:48

1.6K0

发布于 2019-04-18 16:44:48

文章被收录于专栏：java闲聊java闲聊

建表与插入数据
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

常规分页 select s.* from student s limit 1000000,10;
优化分页 select s.* from student s WHERE s.id >= (SELECT s.id FROM student LIMIT 1000000, 1) LIMIT 10;
最优分页 SELECT s.* FROM student s WHERE s.id BETWEEN 1000000 AND 1000010;
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