问题： 构造SQL语句以查找Michael Phelps发送的所有消息。注意：您必须使用WHERE 子句设置此查询的条件。显示以下列： -发件人的名字 -寄件人的姓氏 -收件人的名字 -收件人的姓氏 -讯息编号 - 信息 -邮件时间戳
表格：
SELECT * FROM contact_list;
+---------------+-----------+------------+----------+
| connection_id | person_id | contact_id | favorite |
+---------------+-----------+------------+----------+
| 1 | 1 | 2 | n |
| 2 | 1 | 3 | n |
| 3 | 1 | 4 | n |
| 4 | 1 | 5 | n |
| 5 | 1 | 6 | n |
| 6 | 2 | 1 | y |
| 7 | 2 | 3 | n |
| 8 | 2 | 4 | n |
| 9 | 3 | 1 | y |
| 10 | 3 | 4 | n |
| 11 | 4 | 5 | n |
| 12 | 4 | 6 | n |
| 13 | 5 | 1 | y |
| 14 | 5 | 6 | n |
| 15 | 7 | 1 | y |
| 16 | 7 | 2 | n |
| 17 | 7 | 4 | n |
+---------------+-----------+------------+----------+
17 rows in set (0.00 sec)
SELECT * FROM person;
+-----------+------------+-----------+------------+
| person_id | first_name | last_name | person_age |
+-----------+------------+-----------+------------+
| 1 | Michael | Phelps | |
| 2 | Katie | Ledecky | |
| 3 | Usain | Bolt | |
| 4 | Allyson | Felix | |
| 5 | Kevin | Durant | |
| 7 | Tom | Soyer | 25 |
+-----------+------------+-----------+------------+
6 rows in set (0.00 sec)
SELECT * FROM message;
+------------+-----------+-------------+--------------------------------------------+---------------------+
| message_id | sender_id | receiver_id | message | send_datetime |
+------------+-----------+-------------+--------------------------------------------+---------------------+
| 1 | 1 | 2 | Congrats on winning the 800m Freestyle! | 2016-12-25 09:00:00 |
| 2 | 2 | 1 | Congrats on winning 23 gold medals! | 2016-12-25 09:01:00 |
| 3 | 3 | 1 | You're the greatest swimmer ever | 2016-12-25 09:02:00 |
| 4 | 1 | 3 | Thanks! You're the greatest sprinter ever | 2016-12-25 09:04:00 |
| 5 | 1 | 4 | Good luck on your race | 2016-12-25 09:05:00 |
+------------+-----------+-------------+--------------------------------------------+---------------------+
5 rows in set (0.00 sec)
我的解决方案： 选择sender_id，receiver_id，message_id，消息，send_datetime 来自messages.message 哪里 sender_id = 1;
+-----------+-------------+------------+--------------------------------------------+---------------------+
| sender_id | receiver_id | message_id | message | send_datetime |
+-----------+-------------+------------+--------------------------------------------+---------------------+
| 1 | 2 | 1 | Congrats on winning the 800m Freestyle! | 2016-12-25 09:00:00 |
| 1 | 3 | 4 | Thanks! You're the greatest sprinter ever | 2016-12-25 09:04:00 |
| 1 | 4 | 5 | Good luck on your race | 2016-12-25 09:05:00 |
+-----------+-------------+------------+--------------------------------------------+---------------------+
我这样做正确吗？如何显示发送者和接收者的名字和姓氏？还是我的操作方式正确？
答案 0 :(得分：0)
您可以使用联接获取人名或您想要的任何名称。这是查询
select * from
( select m.messageid,m.senderId,p.first_name as 'senderName' from message m inner join person p on ( p.person_id=m.senderId)
) sen
inner join
( select m.messageid,m.receiver_id,p.first_name as 'receiverName' from message m
inner join person p on ( p.person_id=m.receiver_id)
) rec
on (rec.messageid=sen.messageid)
where sen.senderId=1
这是我创建两个临时表的说明（即，sen用于发送方，rec用于接收方），而不是使用messageId上的内部连接来连接两个表。希望结果表能为您提供所有想要的细节。
答案 1 :(得分：0)
MySQL 5.6模式设置：
create table contact_list(
connection_id int,
person_id int,
contact_id int,
favorite varchar(1)
);
insert into contact_list values (1, 1, 2, 'n');
insert into contact_list values (2, 1, 3, 'n');
insert into contact_list values (3, 1, 4, 'n');
insert into contact_list values (4, 1, 5, 'n');
insert into contact_list values (5, 1, 6, 'n');
insert into contact_list values (6, 2, 1, 'y');
insert into contact_list values (7, 2, 3, 'n');
insert into contact_list values (8, 2, 4, 'n');
insert into contact_list values (9, 3, 1, 'y');
insert into contact_list values (0, 3, 4, 'n');
insert into contact_list values (1, 4, 5, 'n');
insert into contact_list values (2, 4, 6, 'n');
insert into contact_list values (3, 5, 1, 'y');
insert into contact_list values (4, 5, 6, 'n');
insert into contact_list values (5, 7, 1, 'y');
insert into contact_list values (6, 7, 2, 'n');
insert into contact_list values (7, 7, 4, 'n');
create table person (
person_id int,
first_name varchar(200),
last_name varchar(200),
person_age int
);
insert into person values (1, 'Michael', 'Phelps', null);
insert into person values (2, 'Katie', 'Ledecky', null);
insert into person values (3, 'Usain', 'Bolt', null);
insert into person values (4, 'Allyson', 'Felix', null);
insert into person values (5, 'Kevin', 'Durant', null);
insert into person values (7, 'Tom', 'Soyer', 25);
create table message (
message_id int,
sender_id int,
receiver_id int,
message varchar(200),
send_datetime DATETIME
);
insert into message values (1, 1, 2, 'Congrats on winning the 800m Freestyle!', '2016-12-25 09:00:00');
insert into message values (2, 2, 1, 'Congrats on winning 23 gold medals!', '2016-12-25 09:01:00');
insert into message values (3, 3, 1, 'You\'re the greatest swimmer ever', '2016-12-25 09:02:00');
insert into message values (4, 1, 3, 'Thanks! You\'re the greatest sprinter ever', '2016-12-25 09:04:00');
insert into message values (5, 1, 4, 'Good luck on your race', '2016-12-25 09:05:00');
获取这些字段需要做什么：
select
pSender.first_name as 'Sender\'s first name',
pSender.last_name as 'Sender\'s last name',
pReciever.first_name as 'Receiver\'s first name',
pReciever.last_name as 'Receiver\'s last name',
m.message_id as 'Message ID',
m.message as 'Message',
m.send_datetime as 'Message Timestamp'
from
message m
join person pSender on pSender.person_id = m.sender_id
join person pReciever on pReciever.person_id = m.receiver_id
Results ：
| Sender's first name | Sender's last name | Receiver's first name | Receiver's last name | Message ID | Message | Message Timestamp |
|---------------------|--------------------|-----------------------|----------------------|------------|--------------------------------------------|----------------------|
| Katie | Ledecky | Michael | Phelps | 2 | Congrats on winning 23 gold medals! | 2016-12-25T09:01:00Z |
| Usain | Bolt | Michael | Phelps | 3 | You're the greatest swimmer ever | 2016-12-25T09:02:00Z |
| Michael | Phelps | Katie | Ledecky | 1 | Congrats on winning the 800m Freestyle! | 2016-12-25T09:00:00Z |
| Michael | Phelps | Usain | Bolt | 4 | Thanks! You're the greatest sprinter ever | 2016-12-25T09:04:00Z |
| Michael | Phelps | Allyson | Felix | 5 | Good luck on your race | 2016-12-25T09:05:00Z |