Node - postgreSQL(三)

本文主要介绍下 postgreSQL一些稍微复杂的语法。
假设目前有表 cd.facilities、cd.members、cd.bookings，具体表内信息，可进入任务页面，通过 SELECT * FROM 表名;查询表内所有内容，此处不一一赘述。

序号	实现功能	关键语法	实现步骤	完整语句
1	1. 从表 cb.bookings 筛选出 starttime 2. starttime 是表 cd.members 中 surname = 'Farrell' && firstname = 'David'的数据	1.JOIN...ON:两表中取交集，等同于 INNER JOIN ... ON,其他可用 left join, right join 2.AS	1. select b.starttime from cb.bookings as b join cb.members as b on b.memid = m.memid;: 筛选出两表中 memid 一致的数据； 2.where m.surname='Farrell' and m.firstname = 'David';：添加限制条件；	select b.starttime from cd.bookings as b join cd.members as m on b.memid = m.memid where m.surname = 'Farrell' and m.firstname = 'David';
2	1.从表 cd.bookings 筛选出 starttime 、表 cd.facilities 中筛选出 name 2.starttime 的时间范围为 '2012-09021'当天，按照 starttime 排序 3.且 name 的名字为 tennis courts	1. join...on 2.as 3.where 4.like	1.select b.starttime as start, f.name from cd.bookings as b join cd.facilities as f on b.facid = f.facid：筛选出两个表中 facid 相等的数据 2.where f.name like 'Tennis%' AND b.starttime >='2012-09-21' and b.starttime < '2012-09-22'：添加限制条件	select b.starttime as start, f.name from cd.bookings as b join cd.facilities as f on b.facid = f.facid where f.name like 'Tennis%' AND b.starttime < '2012-09-22' and b.starttime >= '2012-09-21' order by b.starttime;
3	1.从表cd.members中筛选出 firstname、surname 2. 筛选出的数据需要满足要求：此条数据的用户推荐过其他用户，及cd.members 中 memid === recommendedby 3.数据按照 surname、firstname 排序 4.数据不能有重复	1.join...on 2.as 3.order by 4.distinct	1.select m1.firstname,m1.surname from cd.members as m1 join cd.members as m2 on m1.memid = m2.recommendedby：初步筛选数据 2.order by surname, firstname：添加排序 3. 在select后添加关键字distinct 过滤重复数据	select distinct m.firstname, m.surname from cd.members as m join cd.members as m2 on m.memid = m2.recommendedby order by surname, firstname;
4	1.从现有的表中列出哪些用户使用过 Tennis Court 2.筛选出 member 作为用户的 firstname + surname，facility 作为场地具体信息 3.按照 member 排序 4.数据不可以重复	1.join...on...join...on 2.as 3.order by 4.distinct 5.in or like 6.主要考察关联多个表，使用 select xx from table1 join table2 on table1.x = table2.y join table3 on table2.xx = table3.yy where ***	1.select * from cd.facilities as f join cd.bookings as b on f.facid = b.facid join cd.members as m on b.memid = m.memid从三个表中筛选中交集数据 2.设置表格数据组成：m.firstname as membre：将 firstname和surname组合成 member 3.where f.facid in (0,1)：筛选出使用过 Tennis court 的数据，也可使用where f.facility like 'Tennis%' 4.order by membre和distinct分别用来排序和过滤重复数据	示例如下：

select distinct m.firstname || ' ' || m.surname as member, f.name as facility
from
    cd.facilities as f join cd.bookings as b 
        on f.facid = b.facid 
    join cd.members as m
        on b.memid = m.memid
    where f.facid in (0,1)
order by member; 

序号	实现功能	关键语法	实现步骤	完整语句
5	1.从表中筛选出 2012-9-14 日预定场地花费大于 30 的用户信息 2.信息包含由fistname和lastname组成的member，场地信息facility和花费的金额 3.按照金额降序排序	1.join...on...join...on 2.case when ... then ... else ... end ... 3.order by、desc	1.过滤数据:select * from cd.facilities as f join cd.bookings as b on f.memid = b.memid join cd.facilities as f on b.facid = f.facid，取交集 2.计算 cost，游客和会员的 cost 不同，case when m.memid = 0 then b.slots * f.guestcost else b.slots * membercost end as cost 3.过滤时间：where b.starttime > '2012-09-14' and b.starttime < '2012-09-15' 4、过滤消费金额：where (m.memid = 0 and b.slots * f.guestcost > 30) or (m.memid != 0 and b.slots * f.membercost > 0) 5. order by cost desc：按照金额降序排序	代码示例如下

select m.firstname || ' ' || m.surname as member,
       f.name as facility,
       case 
        when m.memid = 0 then
          b.slots * f.guestcost
        else 
          b.slots * f.membercost
        end as cost
    from cd.bookings as b
    join cd.members as m
        on b.memid = m.memid
    join cd.facilities as f
        on f.facid = b.facid
where starttime > '2012-09-14' and starttime < '2012-09-15'
and ((m.memid = 0 and b.slots * f.guestcost > 30) or (m.memid != 0 and b.slots * f.membercost > 30))
order by cost desc;

序号	实现功能	关键语法	实现步骤	完整语句
6	1.从cd.members中将用户的推荐人信息列出 2.无推荐人可为空 3.firstname和lastname组成member，为用户信息，recommender也由 fristname和surname组成，为推荐人信息 4.不可使用join...on 5.删除重复数据，按照member排序	1.双重select 2.order、distinct	1.筛选出用户信息:selct distinct m.firstname as member from cd.members as m order by member; 2.在 select 中嵌套 select：selct rec.member from cd.members as rec where rec.memid = m.recommendedby	示例如下

select distinct m.firstname || ' ' || m.surname as member,
    (select rec.firstname || ' ' || rec.surname as recommender 
            from cd.members as rec
        where rec.memid = m.recommendedby
    )
from cd.members as m
order by member;

序号	实现功能	关键语法	实现步骤	完整语句
7	1.实现查询结果如示例5所示 2.使用双重select简化语句	1.双重select	直接看示例

select member, facility, cost from
(select
    m.firstname || ' ' || m.surname as member,
    f.name as facility,
    case when m.memid = 0 
        then b.slots * f.guestcost
        else b.slots * f.membercost
        end
    as cost
from 
    cd.members as m
    join cd.bookings as b on b.memid = m.memid 
    join cd.facilities as f on f.facid = b.facid
where b.starttime > '2012-09-14' and b.starttime < '2012-09-15'
) as bookings
where cost > 30
order by cost desc;

大部分内容主要来自PostgreSQL Exercises。