SQL查询：3个表的最高值加上行的其余部分再加上

Question

i'm currently stuck on a sql-query, trying to find a solution, but making me headache for 2 stays now. i've got 3 tables

user-table:

+-----+----------+-----------+
| pid | username |   role    |
+-----+----------+-----------+
|   1 | user1    | patient   |
|   2 | user2    | patient   |
|   3 | user3    | doc       |
|   4 | user4    | assistant |
|   5 | user5    | patient   |
+-----+----------+-----------+

base-dat:

+-----+---------+-------+------------+
| pid | surname | name  | birthdate  |
+-----+---------+-------+------------+
|   1 | smith   | john  | 1950-07-31 |
|   2 | jackson | sarah | 1948-08-15 |
+-----+---------+-------+------------+

med-dat:

+-----+-----+---------------+--------+--------+
| mid | pid | dateLastEntry | weight | pulse  |
+-----+-----+---------------+--------+--------+
|   1 |   1 | 2017-12-01    |     86 |     65 |
|   2 |   1 | 2017-12-02    |     84 |     70 |
|   3 |   1 | 2017-12-03    |     80 |     67 |
|   4 |   2 | 2017-11-15    |     66 |     60 |
|   5 |   2 | 2017-11-17    |     60 |     64 |
+-----+-----+---------------+--------+--------+

I'm trying to get the max(dateLastEntry) for each user with role patient, showing their pid, name, surname, weight, pulse in a single row - , even if there is no med-data entry for the patient: something like this:

+-----+---------+-------+------------+--------+-------+
| pid | surname | name  | lastEntry  | weight | pulse |
+-----+---------+-------+------------+--------+-------+
|   1 | smith   | john  | 2017-12-02 | 84     | 70    |
|   2 | jackson | sarah | 2017-11-17 | 60     | 64    |
|   5 | NONE    | NONE  | NONE       | NONE   | NONE  |
+-----+---------+-------+------------+--------+-------+

Atm my statement looks like this, but can't get the proper result:

select b.pid, s.surname, s.name, max(m.date) as lastEntry, m.weight, m.pulse
from users b 
left join med-dat m on b.pid = m.pid
left join base-dat s on m.pid = s.pid
where b.role = 'Patient'
group by b.pid, s.surname, s.name, m.weight;

Answer 1

You can rewrite your query as below to get the desired output

select b.pid, s.surname, s.name, m.dateLastEntry as lastEntry, m.weight, m.pulse
from users b 
left join med_dat m on b.pid = m.pid
left join base_dat s on m.pid = s.pid
left join med_dat m1 on m.pid = m1.pid 
                     and m.dateLastEntry < m1.dateLastEntry
where m1.pid is null
and b.role = 'Patient'

DEMO

Edit from comment, join base_dat using pid from user table

select b.pid, s.surname, s.name, m.dateLastEntry as lastEntry, m.weight, m.pulse
from users b 
left join med_dat m on b.pid = m.pid
left join base_dat s on b.pid = s.pid
left join med_dat m1 on m.pid = m1.pid and m.dateLastEntry < m1.dateLastEntry
where m1.pid is null
and b.role = 'Patient'
group by b.pid, s.surname, s.name, m.weight;

Demo