一、基礎記錄資料
常數列的最大值
select max
(article)
as article from shop;
select * from shop where price =
(select max
(article) from shop)
;
select article,
max(price)
as price from shop group
by article;
select article,dealer,price from shop s1 where price=
(select max
(s2.price) from shop s2 where s1.article =s2.article)
;
select @min_price:
=min
(price)
,@max_price:
=max
(price) from shop;
//方法一
select json-
>
>
'$.attr' from table;
//方法二
select json_unquote
(json_extract
(json,
'$.attr'
)) from table;
思路：使用子查詢和諸如min這樣的聚合函式，任意選擇並保留乙個id（次例會保留重覆記錄的最小的id值的記錄）
delete from dupes
where id not in (select min
(id) from dupes
group by name)
時間戳以int值儲存，需要按著時間範圍統計資料
select
count(*
)from vote_votedata where from_unixtime
( create_time) between '2019-04-03 00:00:00'
and'2019-04-04 00:00:00'
;
select
title,
count
(distinct from_user )
,count
(distinct clientip )
, group_hour
from
(select
title,
from_user ,
clientip,
date_format
(from_unixtime
( create_time )
,'%y%m%d%h'
)as group_hour
from
ims_huiyi_weivote_log)
as r1
group
by title,group_hour
資料**兩個表，登入日誌表log_login和班級成員表class_user，兩個表以user_id關聯，日誌表中存在重複登入寫日誌的情況，編寫語句如下
select
count
(distinct user_id)
as login_count
from log_login
where user_id in
(select user_id as id
from class_user
where class_id =1)
;
[1] 吳津津. php與mysql權威指南[m]. 機械工業出版社, 2011.
[2]
[3] 劉春輝譯.sql經典例項[m].人民有點出版社，2018
[4]
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