（全栈须知）8.MYSQL优化总结

1、数据库表结构优化

a.选取最适用的字段属性、索引

根据实际情况：如限制varchar字段长度，设置定长的char；使用enum。

b.使用连接来代替子查询

根据实际情况：能够改写为join的尽量不要使用子查询。
//子查询/left join/left semi join

c.使用explain分析SQL问题

记录慢查询日志，逐条分析。

d.测试

创建测试表：

CREATE TABLE `goods` (
 `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
 `name` varchar(128) COLLATE utf8mb4_general_ci NOT NULL,
 `price` FLOAT(10,3) UNSIGNED NOT NULL DEFAULT '0.000' COMMENT '价格';
 `info` varchar(255) COLLATE utf8mb4_general_ci NOT NULL,
 PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT='商品表';

CREATE TABLE `goods_order_log` (
 `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
 `order_id` int(10) unsigned NOT NULL COMMENT '订单id',
 `buy_time` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '购买时间',
 `goods_id` int(10) unsigned NOT NULL COMMENT '订单id中：商品id',
 `goods_num` int(10) unsigned NOT NULL COMMENT '订单id中：商品id的数量',
 PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT='商品购买流水表';

CREATE TABLE `goods_fav_log` (
 `id` int(10) unsigned NOT NULL AUTO_INCREMENT,
 `user_id` int(10) unsigned NOT NULL COMMENT '搜藏的用户id',
 `goods_id` int(10) unsigned NOT NULL COMMENT '商品id',
 `buy_time` `fav_value` ENUM('1','0') NOT NULL DEFAULT '1' COMMENT '是否搜藏',
 PRIMARY KEY (`id`),
 KEY `user_id` (`user_id`),
 KEY `goods_id` (`goods_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci ROW_FORMAT=COMPACT COMMENT='商品搜藏流水表'

填充测试数据的存储过程：

DELIMITER $$
CREATE PROCEDURE `insert_goods`(IN `c` INT UNSIGNED)
    NO SQL
    COMMENT '生成测试数据的存储过程'
BEGIN
declare i int default 0;
  set autocommit = 0;
  repeat
    set i = i + 1;
    insert into goods(name,price,info) values(concat(i,'_',rand_string(60)),floor(RAND()*100000)/100,rand_string(120));
  until i = c end repeat;
  set autocommit = 1;
END$$

DELIMITER $$
CREATE PROCEDURE `insert_goods_order_log`(IN `c` INT UNSIGNED)
    NO SQL
    COMMENT '生成订单流水的存储过程'
BEGIN
declare i int default 0;
  set autocommit = 0;
  set @basetime = '2016-01-01 00:00:00';
  repeat
    set i = i + 1;
    set @orderid = concat(REPLACE(REPLACE(REPLACE(NOW(),'-',''),' ',''),':',''), '_',rand_string(6));
set @goodsnums = floor(RAND()*10) + 1;
set @buytime = from_unixtime(UNIX_TIMESTAMP(@basetime) + floor((UNIX_TIMESTAMP()-UNIX_TIMESTAMP(@basetime))*RAND()));

  while @goodsnums>0 do
    set @goodid = floor(RAND() * 10000) + 1;
    insert into goods_order_log(order_id,buy_time,goods_id,goods_num) values(@orderid,@buytime,@goodid,RAND()*50);
    set @goodsnums = @goodsnums - 1;
  end while;

  until i = c end repeat;
  set autocommit = 1;
END$$
DELIMITER ;

DELIMITER $$
CREATE PROCEDURE `insert_goods_fav_log`(IN `c` INT UNSIGNED)
    NO SQL
    COMMENT '生成用户搜藏商品的存储过程'
BEGIN
declare i int default 0;
  set autocommit = 0;
  repeat
    set i = i + 1;
    set @userid = floor(RAND()*100000) + 1;
    set @goodsid = floor(RAND()*100000) + 1;
    select @userid,@goodsid,FLOOR(RAND()*2);
    insert into goods_fav_log(user_id,goods_id,fav_value) values(@userid,@goodsid,concat(FLOOR(RAND()*2),''));

  until i = c end repeat;
  set autocommit = 1;
END$$
DELIMITER ;

call insert_goods(10000); //商品表,1w
call insert_goods_order_log(1000000); //订单详情表,100w
call insert_goods_fav_log(100000); //商品收藏表,10w

//(部分商品)区间销量排行
select goods_id,sum(goods_num) as goods_nums from goods_order_log where goods_id between 1 and 199  group by goods_id order by goods_nums desc limit 0,20; 
##销售额排行
//子查询
select a.id,b.goods_nums,a.price,(b.goods_nums*a.price) as goods_sales from goods as a
    inner join (select goods_id,sum(goods_num) as goods_nums from goods_order_log where goods_id between 1 and 1999 group by goods_id ) as b on a.id=b.goods_id
order by goods_sales desc limit 0,20; 

//商品收藏排行
select goods_id,count(id) as fav_nums from goods_fav_log where fav_value='1' group by goods_id order by fav_nums desc limit 0,20; 

2、规范使用

真正好的优化，是需要建立一套施行的标准，在起步时即达到最优。参考：
《MySQL 数据库铁律 2019.09》
《详解Mysql 30条军规》