一、提要

作為一名數(shù)據(jù)工作人員，SQL是日常工作中最常用的數(shù)據(jù)提取&簡(jiǎn)單預(yù)處理語言。因?yàn)槠涫褂玫膹V泛性和易學(xué)程度也被其他崗位比如產(chǎn)品經(jīng)理、研發(fā)廣泛學(xué)習(xí)使用，本篇文章主要結(jié)合經(jīng)典面試題，給出通過數(shù)據(jù)開發(fā)面試的SQL方法與實(shí)戰(zhàn)。以下題目均來與筆者經(jīng)歷&網(wǎng)上分享的中高難度SQL題。

二、解題思路

• 簡(jiǎn)單——會(huì)考察一些group by & limit之類的用法，或者平時(shí)用的不多的函數(shù)比如rand()類；會(huì)涉及到一些表之間的關(guān)聯(lián)

• 中等——會(huì)考察一些窗口函數(shù)的基本用法；會(huì)有表之間的關(guān)聯(lián)，相對(duì)tricky的地方在于會(huì)有一些自關(guān)聯(lián)的使用

• 困難——會(huì)有中位數(shù)或者更加復(fù)雜的取數(shù)概念，可能要求按照某特定要求生成列；一般這種題建中間表會(huì)解得清晰些

三、SQL真題

第一題

• order訂單表，字段為：goods_id， amount ；

• pv 瀏覽表，字段為：goods_id，uid；

• goods按照總銷售金額排序，分成top10,top10~top20,其他三組

求每組商品的瀏覽用戶數(shù)（同組內(nèi)同一用戶只能算一次）

create table if not exists test.nil_goods_category asselect goods_id,case when nn<= 10 then 'top10' ? ? ?when nn<= 20 then 'top10~top20' ? ? ?else 'other' end as goods_groupfrom( ? ?select goods_id ? ?,row_number() over(partition by goods_id order by sale_sum desc) as nn ? ?from ? ?( ? ? ? ?select goods_id,sum(amount) as sale_sum ? ? ? ?from order ? ? ? ?group by 1 ? ?) aa) bb;select b.goods_group,count(distinct a.uid) as numfrom pv a left join test.nil_goods_category b on a.goods_id = b.goods_idgroup by 1;

第二題

商品活動(dòng)表 goods_event，g_id（有可能重復(fù)），t1（開始時(shí)間）,t2（結(jié)束時(shí)間）

給定時(shí)間段（t3,t4)，求在時(shí)間段內(nèi)做活動(dòng)的商品數(shù)

1.select count(distinct g_id) as event_goods_numfrom goods_eventwhere (t1<=t4 and t1>=t3) or (t2>=t3 and t2<=t4)

2.select count(distinct g_id) as event_goods_numfrom goods_eventwhere (t1<=t4 and t1>=t3) union all

第三題

商品活動(dòng)流水表，表名為event，字段：goods_id， time；

求參加活動(dòng)次數(shù)最多的商品的最近一次參加活動(dòng)的時(shí)間

select a.goods_id,a.timefrom event a inner join( ? ?select goods_id,count(*) ? ?from event ? ?group by gooods_id ? ?order by count(*) desc ? ?limit 1) bon a.goods_id = b.goods_idorder by a.goods_id,a.time desc

第四題

用戶登錄的log數(shù)據(jù)，劃定session，同一個(gè)用戶一個(gè)小時(shí)之內(nèi)的登錄算一個(gè)session；

生成session列

drop table if exists koo.nil_temp0222_a2;create table if not exists koo.nil_temp0222_a2 asselect * ? ?,row_number() over(partition by userid order by inserttime) as nn1from( ? ?select a.* ? ?,b.inserttime as inserttime_aftr ? ?,datediff(b.inserttime,a.inserttime) as session_diff ?from ?( ? ?select userid,inserttime ? ? ?,row_number() over(partition by userid order by inserttime asc) nn ? ?from koo.nil_temp0222 ? ?where userid = 1900000169 ?) a ? ?left join ?( ? ? select userid,inserttime ? ? ?,row_number() over(partition by userid order by inserttime asc) nn ? ?from koo.nil_temp0222 ? ?where userid = 1900000169 ?) b ?on a.userid = ?b.userid and a.nn = b.nn-1) aawhere session_diff >10 or nn = 1order by userid,inserttime;

drop table if exists koo.nil_temp0222_a2_1;create table if not exists koo.nil_temp0222_a2_1 asselect a.*,case when b.nn is null then a.nn+3 else b.nn end as nn_endfrom koo.nil_temp0222_a2 a left join koo.nil_temp0222_a2 b on a.userid = b.userid and a.nn1 = b.nn1 - 1;

select a.*,b.nn1 as session_idfrom( ?select userid,inserttime ? ?,row_number() over(partition by userid order by inserttime asc) nn ?from koo.nil_temp0222 ?where userid = 1900000169) aleft join koo.nil_temp0222_a2_1 b on a.userid = b.useridand a.nn>=b.nnand a.nn<b.nn_end

第五題

訂單表，字段有訂單編號(hào)和時(shí)間；

取每月最后一天的最后三筆訂單

select *from( ?select * ?,rank() over(partition by mm order by dd desc) as nn1 ?,row_number() over(partition by mm,dd order by inserttime desc) as nn2 ?from ?(select cast(right(to_date(inserttime),2) as int) as dd,month(inserttime) as mm,userid,inserttime ?from koo.nil_temp0222) aa ) bb where nn1 = 1 and nn2<=3;

第六題

數(shù)據(jù)庫表Tourists，記錄了某個(gè)景點(diǎn)7月份每天來訪游客的數(shù)量如下：

id date visits 1 2017-07-01 100 …… 非常巧，id字段剛好等于日期里面的幾號(hào)。

現(xiàn)在請(qǐng)篩選出連續(xù)三天都有大于100天的日期。

上面例子的輸出為：date 2017-07-01 ……

select a.*,b.num as num2,c.num as num3from table ?a left join table bon a.userid = b.useridand a.dt = date_add(b.dt,-1)left join table con a.userid = c.useridand a.dt = date_add(c.dt,-2)where b.num>100and a.num>100and c.num>100

第七題

現(xiàn)有A表，有21個(gè)列，第一列id，剩余列為特征字段，列名從d1-d20，共10W條數(shù)據(jù)！

另外一個(gè)表B稱為模式表，和A表結(jié)構(gòu)一樣，共5W條數(shù)據(jù)

請(qǐng)找到A表中的特征符合B表中模式的數(shù)據(jù)，并記錄下相對(duì)應(yīng)的id

有兩種情況滿足要求：

• 每個(gè)特征列都完全匹配的情況下

• 最多有一個(gè)特征列不匹配，其他19個(gè)特征列都完全匹配，但哪個(gè)列不匹配未知

1.select aa.*from( ?select *,concat(d1,d2,d3……d20) as mmd ?from table) aa left join( ?select id,concat(d1,d2,d3……d20) as mmd ?from table) bb on aa.id = bb.idand aa.mmd = bb.mmd

2.select a.*,sum(d1_jp,d2_jp……,d20_jp) as same_judgefrom( ?select a.* ?,case when a.d1 = b.d1 then 1 else 0 end as d1_jp ?,case when a.d2 = b.d2 then 1 else 0 end as d2_jp ?,case when a.d3 = b.d3 then 1 else 0 end as d3_jp ?,case when a.d4 = b.d4 then 1 else 0 end as d4_jp ?,case when a.d5 = b.d5 then 1 else 0 end as d5_jp ?,case when a.d6 = b.d6 then 1 else 0 end as d6_jp ?,case when a.d7 = b.d7 then 1 else 0 end as d7_jp ?,case when a.d8 = b.d8 then 1 else 0 end as d8_jp ?,case when a.d9 = b.d9 then 1 else 0 end as d9_jp ?,case when a.d10 = b.d10 then 1 else 0 end as d10_jp ?,case when a.d20 = b.d20 then 1 else 0 end as d20_jp ?,case when a.d11 = b.d11 then 1 else 0 end as d11_jp ?,case when a.d12 = b.d12 then 1 else 0 end as d12_jp ?,case when a.d13 = b.d13 then 1 else 0 end as d13_jp ?,case when a.d14 = b.d14 then 1 else 0 end as d14_jp ?,case when a.d15 = b.d15 then 1 else 0 end as d15_jp ?,case when a.d16 = b.d16 then 1 else 0 end as d16_jp ?,case when a.d17 = b.d17 then 1 else 0 end as d17_jp ?,case when a.d18 = b.d18 then 1 else 0 end as d18_jp ?,case when a.d19 = b.d19 then 1 else 0 end as d19_jp ?from table a ?left join table b ?on a.id = b.id ) aawhere sum(d1_jp,d2_jp……,d20_jp) = 19

第八題

我們把用戶對(duì)商品的評(píng)分用稀疏向量表示，保存在數(shù)據(jù)庫表t里面：

• t的字段有：uid，goods_id，star。uid是用戶id

• goodsid是商品id

• star是用戶對(duì)該商品的評(píng)分，值為1-5

現(xiàn)在我們想要計(jì)算向量?jī)蓛芍g的內(nèi)積，內(nèi)積在這里的語義為：

對(duì)于兩個(gè)不同的用戶，如果他們都對(duì)同樣的一批商品打了分，那么對(duì)于這里面的每個(gè)人的分?jǐn)?shù)乘起來，并對(duì)這些乘積求和。

例子，數(shù)據(jù)庫表里有以下的數(shù)據(jù)：

U0 g0 2
U0 g1 4
U1 g0 3
U1 g1 1

計(jì)算后的結(jié)果為：

U0 U1 23+41=10 ……

select aa.uid1,aa.uid2,sum(star_multi) as resultfrom( ?select a.uid as uid1 ?,b.uid as uid2 ?,a.goods_id ?,a.star * b.star as star_multi ?from t a ?left join t b ?on a.goods_id = b.goods_id ?and a.udi<>b.uid ?) aa group by 1,2

select uid1,uid2,sum(multiply) as resultfrom(select t.uid as uid1, t.uid as uid2, goods_id,a.star*star as multiplyfrom a left join b on a.goods_id = goods_idand a.uid<>uid) aagroup by goods

第九題

給出一堆數(shù)和頻數(shù)的表格，統(tǒng)計(jì)這一堆數(shù)中位數(shù)

select a.*,b.s_mid_n,c.l_mid_n,avg(b.s_mid_n,c.l_mid_n)from( ?select ?case when mod(count(*),2) = 0 then count(*)/2 else (count(*)+1)/2 end as s_mid ?,case when mod(count(*),2) = 0 then count(*)/2+1 else (count(*)+1)/2 end as l_mid ? ?from table) a left join( ?select id,num,row_number() over(partition by id order by num asc) nn ?from table) b on a.s_mid = b.nnleft join( ?select id,num,row_number() over(partition by id order by num asc) nn ?from table) c ?on a.l_mid = c.nn

第十題

表order有三個(gè)字段，店鋪ID，訂單時(shí)間，訂單金額

查詢一個(gè)月內(nèi)每周都有銷量的店鋪

select distinct credit_levelfrom( ?select credit_level,count(distinct nn) as number ?from ?( ? ?select userid,credit_level,inserttime,month(inserttime) as mm ? ?,weekofyear(inserttime) as week ? ?,dense_rank() over(partition by credit_level,month(inserttime) order by weekofyear(inserttime) asc) as nn ? ?from koo.nil_temp0222 ? ?where substring(inserttime,1,7) = '2019-12' ? ?order by credit_level ,inserttime ? ?) aa ?group by 1 ?) bbwhere number = (select count(distinct weekofyear(inserttime))from koo.nil_temp0222 where substring(inserttime,1,7) = '2019-12')

總結(jié)

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