项目上线后,谈一下感触比较深的一点:查询优化

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前言

  开心一刻

    儿子有道题不需要做,喊我过去教他。我推了推一旁的老公:我头疼,你去吧。老公不动,我:零花钱涨一千。话音刚落,老公就屁颠屁颠跑去儿子房间。进去非要几分钟,一声怒吼伴随着儿子的哭声传来的瞬间,老公从儿子房间出来,边走边说:“朽木不可雕也。”儿子从房间探出半个身子,一脸委屈:“爸爸本来 会做,也许给我一块钱,我你可不都都可以明天早点去学校抄同学的。还我你可不都都可以无须告诉你,我不肯,他就吼我。”

现象背景

  前段时间,被紧急调到另另一个 新项目,支撑新项目的开发。跌跌撞撞之下,项目也正常上线了,期间收获颇多,无论是业务上的,还是业务之外的。业务上的就太多说了,不具通用性,意义不大,有好多好多 业务之外的东东给我的感触比较深,特记录下来,与其他同学分享下 : 查询优化

查询优化

  完整版示例工程:data-init,包括数据库表的 ddl 和 dml,以及数据批量的生成

  相关表

    涉及的表太多,一共三张:额度表、记录表 、 存款表

    额度表 t_custmor_credit

CREATE TABLE t_customer_credit (
  id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主键',
  login_name VARCHAR(1000) NOT NULL COMMENT '名称',
    credit_type TINYINT(1) NOT NULL COMMENT '额度类型,1:自由资金,2:冻结资金,3:优惠',
    amount DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '额度值',
    create_by VARCHAR(1000) NOT NULL COMMENT '创建者',
    create_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    update_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '创建时间',
    update_by VARCHAR(1000) NOT NULL COMMENT '修改者',
  PRIMARY KEY (id)
);
View Code

      记录每个顾客的当前额度,额度一共分并都有:自由资金、冻结资金和优惠,也本来 说每个顾客会有 3 条记录来表示他的各个额度。表中数据如下

    额度记录 t_custmor_credit_record

CREATE TABLE t_customer_credit_record (
  id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主键',
  login_name VARCHAR(1000) NOT NULL COMMENT '名称',
    credit_type TINYINT(1) NOT NULL COMMENT '额度类型,参考t_custmor_credit的credit_type',
    bill_no VARCHAR(1000) NOT NULL COMMENT '订单号',
    amount_before DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '前额度值',
    amount_change DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '额度变化值',
    amount_after DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '后额度值',
    create_by VARCHAR(1000) NOT NULL COMMENT '创建者',
    create_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    remark VARCHAR(10000) NOT NULL DEFAULT '' COMMENT '备注',
  PRIMARY KEY (id)
);
View Code

      记录顾客额度的每一次变化,而且有额度变化(不管是哪个额度进行了变化),过后新增3条记录,每个类型的额度过后新增第一根记录。另外,该表只会有数据的插入,不需要有数据的删、改。表中数据如下

    存款表 t_custmor_deposit

CREATE TABLE t_customer_deposit (
  id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主键',
  login_name VARCHAR(1000) NOT NULL COMMENT '名称',
    bill_no VARCHAR(1000) NOT NULL COMMENT '订单号',
    amount DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '存款金额',
    deposit_state TINYINT(1) NOT NULL COMMENT '存款情况汇报: 1成功,2失败,3未知',
    channal TINYINT(2) NOT NULL COMMENT '存款渠道: 1:银联,2支付宝,3微信',
    create_by VARCHAR(1000) NOT NULL COMMENT '创建者',
    create_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    remark VARCHAR(10000) NOT NULL DEFAULT '' COMMENT '备注',
  PRIMARY KEY (id)
);
View Code

      记录顾客的每一次存款,该表只会有数据的插入,不需要有数据的删、改。表中数据如下

  产品需求

    分页展示如下列表(具体的过滤条件就不列了,其他同学就当是初始情况汇报,还未输入过滤条件)

     实现比较简单,t_custmor_credit_record 左关联 t_custmor_deposit 就好,而且其他同学的额度记录表与需求列表好多好多 许的出入,需用做一下简单的行转列。

  需求实现

    其他同学先来看看最初的SQL查询,这肯能是好多好多 人最容易想到的

SELECT MIN(tcd.channal) channal, MAX(tccr.id) mId,tccr.login_name,tccr.bill_no,tccr.create_time,
    IF(credit_type=1,amount_before,0) AS freeBefore,
    IF(credit_type=1,amount_change,0) AS freeChange,
    IF(credit_type=1,amount_after,0) AS freeAfter,
    IF(credit_type=2,amount_before,0) AS freezeBefore,
    IF(credit_type=2,amount_change,0) AS freezeChange,
    IF(credit_type=2,amount_after,0) AS freezeAfter,
    IF(credit_type=3,amount_before,0) AS promotionBefore,
    IF(credit_type=3,amount_change,0) AS promotionChange,
    IF(credit_type=3,amount_after,0) AS promotionAfter
FROM t_customer_credit_record tccr
LEFT JOIN t_customer_deposit tcd ON tccr.bill_no = tcd.bill_no
GROUP BY tccr.bill_no,tccr.login_name,tccr.create_time
ORDER BY mId desc
LIMIT 0, 10;
View Code

    数据量少的前一天,也许能在其他同学接受的时间内查出其他同学需用的结果,一旦数据量多了,这俩 SQL就跑不动了;其他同学先看下 1000w 数据的情况汇报下,其他同学只进行 t_custmor_credit_record 单表查询

SELECT MAX(id) mId,login_name,bill_no,create_time,
    IF(credit_type=1,amount_before,0) AS freeBefore,
    IF(credit_type=1,amount_change,0) AS freeChange,
    IF(credit_type=1,amount_after,0) AS freeAfter,
    IF(credit_type=2,amount_before,0) AS freezeBefore,
    IF(credit_type=2,amount_change,0) AS freezeChange,
    IF(credit_type=2,amount_after,0) AS freezeAfter,
    IF(credit_type=3,amount_before,0) AS promotionBefore,
    IF(credit_type=3,amount_change,0) AS promotionChange,
    IF(credit_type=3,amount_after,0) AS promotionAfter
FROM t_customer_credit_record
GROUP BY bill_no,login_name,create_time
ORDER BY mId desc
LIMIT 0, 10;
View Code

    效果如下

    花了近 8 秒,这还本来 单表,肯能执行上方的联表SQL,那时间又得增加不少(我试验的结果是直接卡住了,看非要查询结果);

  优化正确处理

    加索引

      查询慢的前一天,其他同学最容易想到的优化法律措施往往本来 加索引;上述SQL执行的前一天,t_custmor_credit_record 和 t_custmor_deposit都没法建索引(主键索引除外),没法其他同学就加索引呗。我的项目中加的是唯一索引,做了唯一约束,前一天这里也加唯一索引

ALTER TABLE t_customer_credit_record ADD UNIQUE uk_unique (bill_no,login_name,create_time,credit_type);
ALTER TABLE t_customer_deposit ADD UNIQUE uk_billno (bill_no);

      此时其他同学看下SQL执行效果

      其他同学发现,t_custmor_credit_record 单表查询的速度几乎没变,将近 8 秒,但 t_custmor_credit_record 与 t_custmor_deposit 联表的查询却在 11 秒内有结果了。加了索引为哪此还没法慢了? 难道没走索引?

      其他同学是都有发现了哪此? IF函数对联表查询算不算走索引有影响,也对单表的查询速度有影响。上图中的 t_custmor_credit_record 单表查询,有IF函数,查询时间近 8 秒,没法IF函数,查询时间 2 秒左右;t_custmor_credit_record 与 t_custmor_deposit 联表查,有IF函数,t_custmor_credit_record 走的是全表查,查询时间近 11 秒,没法IF函数,t_custmor_credit_record 走的是索引,查询时间 3 秒非要。没法其他同学有没法哪此法律措施拿掉这俩 IF函数呢?

    使用 CASE...WHEN....THEN 代替 IF

SELECT MAX(id) mId,login_name,bill_no,create_time,
    CASE credit_type WHEN 1 THEN amount_before ELSE 0 END AS freeBefore,
    CASE credit_type WHEN 1 THEN amount_change ELSE 0 END AS freeChange,
    CASE credit_type WHEN 1 THEN amount_after ELSE 0 END AS freeAfter,
    CASE credit_type WHEN 2 THEN amount_before ELSE 0 END AS freeChange,
    CASE credit_type WHEN 2 THEN amount_change ELSE 0 END AS freeChange,
    CASE credit_type WHEN 2 THEN amount_after ELSE 0 END AS freeChange,
    CASE credit_type WHEN 3 THEN amount_before ELSE 0 END AS promotionBefore,
    CASE credit_type WHEN 3 THEN amount_change ELSE 0 END AS promotionChange,
    CASE credit_type WHEN 3 THEN amount_after ELSE 0 END AS promotionAfter
FROM t_customer_credit_record
GROUP BY bill_no,login_name,create_time
ORDER BY mId desc
LIMIT 0, 10;

SELECT MIN(tcd.channal) channal, MAX(tccr.id) mId,tccr.login_name,tccr.bill_no,tccr.create_time,
    CASE credit_type WHEN 1 THEN amount_before ELSE 0 END AS freeBefore,
    CASE credit_type WHEN 1 THEN amount_change ELSE 0 END AS freeChange,
    CASE credit_type WHEN 1 THEN amount_after ELSE 0 END AS freeAfter,
    CASE credit_type WHEN 2 THEN amount_before ELSE 0 END AS freeChange,
    CASE credit_type WHEN 2 THEN amount_change ELSE 0 END AS freeChange,
    CASE credit_type WHEN 2 THEN amount_after ELSE 0 END AS freeChange,
    CASE credit_type WHEN 3 THEN amount_before ELSE 0 END AS promotionBefore,
    CASE credit_type WHEN 3 THEN amount_change ELSE 0 END AS promotionChange,
    CASE credit_type WHEN 3 THEN amount_after ELSE 0 END AS promotionAfter
FROM t_customer_credit_record tccr
LEFT JOIN t_customer_deposit tcd ON tccr.bill_no = tcd.bill_no
GROUP BY tccr.bill_no,tccr.login_name,tccr.create_time
ORDER BY mId desc
LIMIT 0, 10;
View Code

      其他同学需用看到,执行时间与 IF 所差无几,执行计划也是与 IF 的一致,这也就反映出都有 IF的现象,应该是 GROUP BY 的现象。其他同学用 GROUP BY 结合 IF(或 CASE...WHEN....THEN),本来 为了将 3 条额度记录合并成第一根、行转列前一天输出其他同学你可不都都可以的结果,那有没法不需要 GROUP BY、又能实现其他同学需求的法律措施了?

    自联代替 GROUP BY

      其他同学再仔细琢磨下这俩 需求,咋一看,嘴笨 需用行转列,没法就需用用到 GROUP BY,没法速度也就低了,这似乎是无解了? 真的非要行转列吗,假设其他同学将额度记录拆分成 3 张表:一张表只存自由资金的额度变化、一张表只存冻结资金的额度变化、一张表只存优惠的额度变化,前一天是都有只需用联表查而无须用 GROUP BY 来进行行转列了? 有小伙伴有肯能会问:t_custmor_credit_record 表肯能定了,数据都跑了不少了,再将其进行拆分,既要改表(同需用用迁移数据),需用改代码,工程量会很大! 其他同学换个高度来看 t_custmor_credit_record ,目前它是 3 中额度记录的另另一个 总和表,其他同学需用从它的身上做文章,变化出其他同学你可不都都可以的那 3 张表,而且进行联表查询呢? 肯定需用的,之类如下

-- 自由资金额度记录表
SELECT * FROM t_customer_credit_record WHERE credit_type = 1;
-- 冻结资金额度记录表
SELECT * FROM t_customer_credit_record WHERE credit_type = 2;
-- 优惠额度记录表
SELECT * FROM t_customer_credit_record WHERE credit_type = 3;

      接下来的 SQL 为啥写,我你可不都都可以其他同学都知道了吧,自联就行了,写法有好多好多 种,常见的写法有如下 4 种

-- 不需要group by,做法1, 好多好多

人比较推荐, 但此种法律措施不支持存款表的过滤条件
SELECT d.channal,a.amount_before AS freeBefore,a.amount_change AS freeChange, a.amount_after freeAfter,
    b.amount_before AS freezeBefore,b.amount_change AS freezeChange, b.amount_after freezeAfter,
    c.amount_before AS promotionBefore,c.amount_change AS promotionChange, c.amount_after promotionAfter
FROM (
    SELECT * FROM t_customer_credit_record WHERE credit_type = 1 ORDER BY id DESC LIMIT 0, 10
) a
LEFT JOIN t_customer_credit_record b ON a.bill_no = b.bill_no AND b.credit_type = 2
LEFT JOIN t_customer_credit_record c ON a.bill_no = c.bill_no AND c.credit_type = 3
LEFT JOIN t_customer_deposit d ON a.bill_no = d.bill_no;

-- 不需要group by,做法2, 此种法律措施支持存款表的过滤条件
SELECT a.channal,a.amount_before AS freeBefore,a.amount_change AS freeChange, a.amount_after freeAfter,
    b.amount_before AS freezeBefore,b.amount_change AS freezeChange, b.amount_after freezeAfter,
    c.amount_before AS promotionBefore,c.amount_change AS promotionChange, c.amount_after promotionAfter
FROM (
    SELECT r.*,d.channal FROM t_customer_credit_record r LEFT JOIN t_customer_deposit d ON r.bill_no = d.bill_no
    WHERE r.credit_type = 1 ORDER BY r.id DESC LIMIT 0, 10
) a
LEFT JOIN t_customer_credit_record b ON a.bill_no = b.bill_no AND b.credit_type = 2
LEFT JOIN t_customer_credit_record c ON a.bill_no = c.bill_no AND c.credit_type = 3;

-- 不需要group by,做法3, 这是最容易想到的法律措施
SELECT d.channal,a.amount_before AS freeBefore,a.amount_change AS freeChange, a.amount_after freeAfter,
    b.amount_before AS freezeBefore,b.amount_change AS freezeChange, b.amount_after freezeAfter,
    c.amount_before AS promotionBefore,c.amount_change AS promotionChange, c.amount_after promotionAfter
FROM t_customer_credit_record a
LEFT JOIN t_customer_credit_record b ON a.bill_no = b.bill_no
LEFT JOIN t_customer_credit_record c ON a.bill_no = c.bill_no
LEFT JOIN t_customer_deposit d ON a.bill_no = d.bill_no
WHERE a.credit_type = 1 AND b.credit_type = 2 AND c.credit_type = 3 
ORDER BY a.id DESC LIMIT 0, 10;

-- 不需要group by,做法4
SELECT d.channal,a.amount_before AS freeBefore,a.amount_change AS freeChange, a.amount_after freeAfter,
    b.amount_before AS freezeBefore,b.amount_change AS freezeChange, b.amount_after freezeAfter,
    c.amount_before AS promotionBefore,c.amount_change AS promotionChange, c.amount_after promotionAfter
FROM t_customer_credit_record a
LEFT JOIN t_customer_credit_record b ON a.bill_no = b.bill_no AND b.credit_type = 2
LEFT JOIN t_customer_credit_record c ON a.bill_no = c.bill_no AND c.credit_type = 3
LEFT JOIN t_customer_deposit d ON a.bill_no = d.bill_no
WHERE a.credit_type = 1 
ORDER BY a.id DESC LIMIT 0, 10;
View Code

      执行结果如下

      就目前的数据量而言,4 种写法的速度一样,而且数据量再往上走,它们前一天还是有性能差别的,其他同学需用仔细看看这 4 个 SQL 的执行计划,它们之间还是有区别的。最终我的项目中采用的是第并都有写法

    表重新设计

      其他同学回过头去看看 t_customer_credit 和 t_custmor_credit_record,算不算真的有必要用 3 条记录来存放顾客的 3 种额度,第一根记录将用户的 3 种额度都记录下来都有更好吗? 如下所示

-- 自认为更好的表设计
DROP TABLE IF EXISTS t_customer_credit_plus;
CREATE TABLE t_customer_credit_plus (
  id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主键',
  login_name VARCHAR(1000) NOT NULL COMMENT '登录名',
    free_amount DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '自由资金额度',
    freeze_amount DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '冻结资金额度',
    promotion_amount DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '优惠资金额度',
    create_by VARCHAR(1000) NOT NULL COMMENT '创建者',
    create_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    update_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '创建时间',
    update_by VARCHAR(1000) NOT NULL COMMENT '修改者',
  PRIMARY KEY (id),
  UNIQUE KEY `uk_login_name` (`login_name`)
);
DROP TABLE IF EXISTS t_customer_credit_record_plus;
CREATE TABLE t_customer_credit_record_plus (
  id INT(11) UNSIGNED NOT NULL AUTO_INCREMENT COMMENT '自增主键',
  login_name VARCHAR(1000) NOT NULL COMMENT '登录名',
    bill_no VARCHAR(1000) NOT NULL COMMENT '订单号',
    free_amount_before DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '自由资金前额度值',
    free_amount_change DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '自由资金前额度变化值',
    free_amount_after DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '自由资金前后额度值',
    freeze_amount_before DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '冻结资金前额度值',
    freeze_amount_change DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '冻结资金额度变化值',
    freeze_amount_after DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '冻结资金后额度值',
    promotion_amount_before DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '优惠前额度值',
    promotion_amount_change DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '优惠额度变化值',
    promotion_amount_after DECIMAL(22,6) NOT NULL DEFAULT '0.00000' COMMENT '优惠后额度值',
    create_by VARCHAR(1000) NOT NULL COMMENT '创建者',
    create_time DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
    remark VARCHAR(10000) NOT NULL DEFAULT '' COMMENT '备注',
  PRIMARY KEY (id),
  UNIQUE KEY `uk_unique` (`bill_no`,`login_name`,`create_time`)
);
View Code

      我你可不都都可以好多好多 人过后有相同的感觉吧,而且从拓展性出发,分 3 条记录的做法更好,为哪此呢? 肯能后续新增 1 种或多种另外的额度类型,上述的 1 条记录的表设计就需用新增字段来适配了, 而且 3 条记录的做法,只需用拓展credit_type的值就好了,表不需要改动。各有利弊,要怎样选着,需用团队协商前一天做出最好的选着。

      最终项目中采用的还是 3 条记录存放 3 个额度的法律措施,没法采用也许的;意味着着是:其他同学都认为速度影响不大,也容易理解,关键是拓展性很好,后续很方便就能加入新的额度类型。

    业务上的协调

      最后其他同学再回到需求上来,这俩 存款渠道 真的有必要显示在额度记录吗?

      1、对公司来说,存款记录太多,那肯定是越好,但其他同学从实际出发,存款记录在额度记录中占的比例大吗,这俩 相信其他同学也都能想象得到,比例非常低,肯能 1000 条记录中会有 1 条;

      2、前一天都有单独的存款页面展示顾客的存款,去专门的存款记录页面看岂都有更直观?

      最后和产品讨论,还真把这俩 列给拿掉了,没法其他同学也就不需用关联存款表来查了,SQL 更简单,速度也更高了!

总结

  1、Oracle 的 DECODE 与 Mysql 中的 IF 都有 CASE 表达式的复杂函数,具有特殊性(非要 Oracle 才认识 DECODE、非要 Mysql 才认识 IF),而都有标准的 SQL,CASE 表达式是标准 SQL 所承认的功能;

  2、SQL 行转列,往往是 GROUP BY 配合聚合函数(SUM、MAX、MIN等)来实现,当然也包括 IF 和 CASE...WHEN....THEN; 

  3、索引是提高查询速度的最有效的、也是最常用的法律措施,其他同学对查询的优化都有往索引上靠,EXPLAIN 需用查看SQL的执行计划,其他同学需用从中获取SQL优化的提示;

  4、一定要结合业务来写出高效的SQL

    肯能好多好多 小伙伴会有前一天的不满:上述的 3 个额度的例子很重特殊,不具备通用性,上述高效的SQL也本来 在你(楼主)的项目中含效。也许的对,而且其他同学要知道,技术并都有本来 用来服务业务的,脱离了业务,技术有哪此实际意义? 而且其他同学回过头去细看,我举的例子真的就特殊到独一无二? 我你可不都都可以还算比较通用吧,还是能套用好多好多 场景的。

  5、要敢于质疑需求

    嘴笨 大多数前一天产品都考虑比较周到,但本来 能完整版保证他没法不犯迷糊的前一天吧。有疑惑就向产品问清楚,其他同学实现的也减慢、更准确。一定无须对现象藏着掖着,以我亲身经历来讲,好多好多 前一天开发认为的都有对的,肯能藏着掖着,那你就准备返工改成你前一天认为的那样吧!