一个分组查询引发的思考

2022-01-05 14:44:44 浏览数 (1)

一个分组查询引发的思考

我们在看项目代码或者SQL语句时, 往往会看到很多非常复杂的业务或者SQL 那么问题来了. 复杂SQL是如何写成的? 下面通过一个数据展示的需求来体会到复杂的SQL是如何书写的

1. 计算平均等待时间

当你拿到需求是一般都是比较简单的, 例如统计某些数据, eg: 统计每天平均等待时间

代码语言：javascript复制
-- 计算平均等待时间
-- 逻辑
select 等待总时间/等待数 as 列名
from 表名
where 时间(后续根据要求可改为按年月日查询)
between 起始时间
and 结束时间
group by 业务名称

-- eg
select businame,
round(sum(waitingTime)/count(case when `state`=2 or 3 then 1 else null end)/60,1) as avgWaitingTime
from t_number_takers 
where DATE_FORMAT(takeTime,'%Y-%m-d%')
BETWEEN  '2021-01-01 00:00:00'
AND  '2021-12-31 23:59:59'
group by businame

2. 分组统计各项业务

下面产品经理又给你说, 那你搞个按年月日进行统计吧, 这样用户可以按照年月日进行统计各种信息

代码语言：javascript复制
-- 通过时间分组(年月日)并根据分组显示每天时长
-- 逻辑
select 各项业务
from 表名
where 时间(后续根据要求可改为按年月日查询)
between 起始时间
and 结束时间
group by 时间

-- eg: 按日分组查询
select  DATE_FORMAT(takeTime,'%Y-%m-%d') as '时间',
round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长(min)',
round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
sum(case when `id` is not null then 1 else null end) as '业务总数',
sum(case when businame ='开户' then 1 else null end) as '开户',
sum(case when businame ='缴费' then 1 else null end) as '缴费',
sum(case when businame ='业务' then 1 else null end) as '业务',
sum(case when businame ='销户' then 1 else null end) as '销户'
from t_number_takers
WHERE 1=1
and takeTime
BETWEEN  '2021-01-01 00:00:00'
AND  '2021-12-31 23:59:59'
group by DATE_FORMAT(takeTime,'%Y-%m-%d')

-- eg: 按月分组查询(见下图)
select  DATE_FORMAT(takeTime,'%Y-%m') as '时间',
round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长(min)',
round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
sum(case when `id` is not null then 1 else null end) as '业务总数',
sum(case when businame ='开户' then 1 else null end) as '开户',
sum(case when businame ='缴费' then 1 else null end) as '缴费',
sum(case when businame ='业务' then 1 else null end) as '业务',
sum(case when businame ='销户' then 1 else null end) as '销户'
from t_number_takers
WHERE 1=1
and takeTime
BETWEEN  '2021-01-01 00:00:00'
AND  '2021-12-31 23:59:59'
group by DATE_FORMAT(takeTime,'%Y-%m')

-- eg: 按年分组查询
select  DATE_FORMAT(takeTime,'%Y') as '时间',
round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长(min)',
round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
sum(case when `id` is not null then 1 else null end) as '业务总数',
sum(case when businame ='开户' then 1 else null end) as '开户',
sum(case when businame ='缴费' then 1 else null end) as '缴费',
sum(case when businame ='业务' then 1 else null end) as '业务',
sum(case when businame ='销户' then 1 else null end) as '销户'
from t_number_takers
WHERE 1=1
and takeTime
BETWEEN  '2021-01-01 00:00:00'
AND  '2021-12-31 23:59:59'
group by DATE_FORMAT(takeTime,'%Y')

ps: 按照时间段(年月日)进行显示时, 用到了 DATE_FORMAT() 函数, 这个改动会对后面的统计带来意想不到的影响

3. 将汇总和统计写在一张表

这个时候, 产品经理又又提出需求了, 需要将汇总信息写在一个接口中返回.

代码语言：javascript复制
-- a.利用 with rollup 进行汇总, 图1. 我们可以看到汇总的那一行为空值
select  DATE_FORMAT(takeTime,'%Y-%m') as '时间',
round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长(min)',
round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
sum(case when `id` is not null then 1 else null end) as '业务总数',
sum(case when businame ='开户' then 1 else null end) as '开户',
sum(case when businame ='缴费' then 1 else null end) as '缴费',
sum(case when businame ='业务' then 1 else null end) as '业务',
sum(case when businame ='销户' then 1 else null end) as '销户'
from t_number_takers
WHERE 1=1
and takeTime
BETWEEN  '2021-01-01 00:00:00'
AND  '2021-12-31 23:59:59'
group by DATE_FORMAT(takeTime,'%Y-%m')
with rollup


-- b.解决为空的情况, 利用 ifnull()函数
 ifnull(列名,'列名为空后的字段') as 列名 <=> 当前列下如果有数据为null,就将该列下这一行null改为: 列名为空后的字段

--  当该列不为函数时, 如图2
select ifnull(businame,'总计') as businame,count(1) as busiNum
from t_number_takers
WHERE DATE_FORMAT(takeTime,'%Y-%m-d%')
BETWEEN  '2021-01-01 00:00:00'
AND  '2021-12-31 23:59:59'
group by businame  with rollup 

-- 当列为函数时会报错, 如下代码  ifnull(DATE_FORMAT(takeTime,'%Y-%m'),"合计") as '时间'
select  ifnull(DATE_FORMAT(takeTime,'%Y-%m'),"合计") as '时间',
round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长(min)',
round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
sum(case when `id` is not null then 1 else null end) as '业务总数',
sum(case when businame ='开户' then 1 else null end) as '开户',
sum(case when businame ='缴费' then 1 else null end) as '缴费',
sum(case when businame ='业务' then 1 else null end) as '业务',
sum(case when businame ='销户' then 1 else null end) as '销户'
from t_number_takers
WHERE 1=1
and takeTime
BETWEEN  '2021-01-01 00:00:00'
AND  '2021-12-31 23:59:59'
group by DATE_FORMAT(takeTime,'%Y-%m')
with rollup

> 1055 - Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'callmachine.t_number_takers.takeTime' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
原因是: MySQL 5.7.5及以上功能依赖检测功能。
如果启用了ONLY_FULL_GROUP_BY SQL模式（默认情况下），MySQL将拒绝选择列表，
HAVING条件或ORDER BY列表的查询引用在GROUP BY子句中既未命名的非集合列，也不在功能上依赖于它们。
（5.7.5之前，MySQL没有检测到功能依赖关系，默认情况下不启用ONLY_FULL_GROUP_BY


-- c.根据b后面出现的问题进行解决, 执行第一条指令(当前shell生效), 然后再执行b中出现问题的语句, 图3.  
-- 可以看到虽然执行没问题, 但是返回结果却没有根据ifnull将 takeTime 为null时的字段改成 我们想要定制的字段: 总计
-- 分组异常时执行下面命令
set sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'
-- 还原之前设置
set sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'
-- 查询当前sql模式
SELECT @@sql_mode



-- d 利用 union all 进行组合查询, 通过组合查询将总计信息拼在原来的列下(图4)
-- 虽然这样写不太规范(在时间里面返回了一个总计的字段, 但是满足了一张表返回所有分组信息和总计结果)
select  DATE_FORMAT(takeTime,'%Y-%m') as '时间' ,
round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长',
round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
sum(case when `id` is not null then 1 else null end) as '业务总数',
sum(case when businame ='开户' then 1 else null end) as '开户',
sum(case when businame ='缴费' then 1 else null end) as '缴费',
sum(case when businame ='业务' then 1 else null end) as '业务',
sum(case when businame ='销户' then 1 else null end) as '销户'
from t_number_takers
where 1=1
and takeTime
between  '2021-01-01 00:00:00'
and  '2021-12-31 23:59:59'
group by DATE_FORMAT(takeTime,'%Y-%m')
union all select
'总计' as '时间' ,
round(sum(waitingTime)/60,1) as "客户平均等待时长",
round(sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/60,1) as '业务平均办理时长',
count(1) as '业务总数',
sum(case when businame ='开户' then 1 else null end) as '开户',
sum(case when businame ='缴费' then 1 else null end) as '缴费',
sum(case when businame ='业务' then 1 else null end) as '业务',
sum(case when businame ='销户' then 1 else null end) as '销户'
from t_number_takers

图1

图2

图3

图4

union和union all区别 union all只是合并查询结果，并不会进行去重和排序操作，在没有去重的前提下，使用union all的执行效率要比union高

ps: 后续因为某些原因, 总计还是单独作为一个接口来了, 尴尬~~~

4. 按照任意字段排序

产品又又又有要求, 让页面显示的统计信息可以根据某个字段进行任意排序

代码语言：javascript复制
 <!--利用mybaties的${}输出, 对其进行任意字段排序 order by ${param3(排序字段)} ${param4(升序降序asc,desc)} -->
   <select id="statisticalBusinessByYear" resultType="map">
       select  DATE_FORMAT(takeTime,'%Y') as '时间' ,
       round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长',
       round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
       sum(case when `id` is not null then 1 else null end) as '业务总数',
	sum(case when businame ='开户' then 1 else null end) as '开户',
	sum(case when businame ='缴费' then 1 else null end) as '缴费',
	sum(case when businame ='业务' then 1 else null end) as '业务',
	sum(case when businame ='销户' then 1 else null end) as '销户'
       from t_number_takers
       where 1=1
       <if test="param1 != null and param1 != ''">
           <if test="param2 != null and param2 != ''">
               and takeTime
               between  #{param1,jdbcType=VARCHAR}
               and  #{param2,jdbcType=VARCHAR}
           </if>
       </if>
       group by DATE_FORMAT(takeTime,'%Y') 
       order by ${param3} ${param4}
   </select>

5. 动态查询列信息

之前按照产品原型写的业务列统计, 如 业务总数/开户/销户/业务/缴费都是根据原型图写的. 产品又不干了. 说万一后面客户增加了其他列的话, 你这种固定显示的业务列统计怎么合乎规范呢? 好吧, 我们继续改. 不慌. 动态查询列信息核心逻辑: 在原来的基础上, 首先新增一个获取所有业务列的接口, 然后在当前查询Dao接口传入这个list. mapper.xml 中 通过使用 mybaties的 < foreach >标签进行遍历

首先看下臃肿的dao层接口

代码语言：javascript复制
List<String> queryBusinessList();

List<Map<String, Object>> statisticalBusinessByMounth(@Param("startTime") String startTime, @Param("endTime") String endTime,
                                                      @Param("statisticalBusinessType") String statisticalBusinessType,
                                                      @Param("sortType") String sortType,@Param("list") List<String> businessList);

mapper.xml下对应的查询语句

代码语言：javascript复制
<select id="queryBusinessList" resultType="java.lang.String">
    select distinct(businame) from t_number_takers
</select>
    
<select id="statisticalBusinessByMounth" resultType="map">
        select  DATE_FORMAT(takeTime,'%Y-%m') as '时间' ,
        round((sum(waitingTime)/count(case when `state` in(2,3) then 1 else null end))/60,1) as '客户平均等待时长',
        round((sum(UNIX_TIMESTAMP(endTime) - UNIX_TIMESTAMP(acceptTime))/count(case when `state`in (2,3) then 1 else null end)/60),1) as '业务平均办理时长',
        sum(case when `id` is not null then 1 else null end) as '业务总数'
        <if test="list != null and list.size() != 0">
            ,
            <foreach collection="list" item="item" separator=",">
                sum(case when businame = #{item} then 1 else null end) as #{item,jdbcType=VARCHAR}
            </foreach>
        </if>
        from t_number_takers
        where 1=1
        <if test="param1 != null and param1 != ''">
            <if test="param2 != null and param2 != ''">
                and takeTime
                between  #{param1,jdbcType=VARCHAR}
                and  #{param2,jdbcType=VARCHAR}
            </if>
        </if>
        group by DATE_FORMAT(takeTime,'%Y-%m')
        order by ${param3} ${param4}
    </select>

总结:

虽然上面的例子可能不如你在其他项目中看到的其他项目那么复杂. 就个人经历而言, 复杂的SQL语句或者业务, 不是一下子就写成的, 而是随着业务的复杂之后, 慢慢的优化而成的. 我们不要过于的惧怕这些复杂的代码, 应该在战略上蔑视它, 在战术上重视它. 多多磨练自己的技巧, 并且及时反思, 而这些行为一定会给你带来意想不到的收获~~~

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