SQL：GROUP BY id 具有最大日期

Question

I have two tables:

Table 1:
worker_number, first_name , last_name , clinic , doctor_type

1   BB BB  Z2 ENT
10  CC CC  Z3 ENT
4   DD DD Z4    Orthopedist
5   EE EE Z5Surgeon
8   AA AA Z1 ENT


Table 2:
worker_number, first_name , last_name , clinic , doctor_type, dt_date, patient_id

'1', 'BB', 'BB', 'Z2', 'ENT', '2017-02-01 10:00:00', '1'
'1', 'BB', 'BB', 'Z2', 'ENT', '2017-02-27 15:20:00', '1'
'8', 'AA', 'AA', 'Z1', 'ENT', '2017-02-28 08:40:00', '1'

Basically i want to get all rows from table 1 that doctor_type = "A" ordered by the dt_date from table 2 which has same worker_number and doctor_type

i tried to do somthing like:

SELECT `table 1`.worker_number, `table 1`.first_name, `table 1`.last_name, `table 1`.clinic
FROM `health`.`table 1`
LEFT JOIN `health`.`table 2`
ON `health`.`table 1`.worker_number = `health`.`table 2`.worker_number
order by `health`.`table 2`.dt_date desc

But i got the following output:

8   AA  AA  Z1
1   BB  BB  Z2
10  CC  CC  Z3
1   BB  BB  Z2
3   DD  DD  Z4
5   EE  EE  Z5

It works really good except for the BB is showing twice, How can i do group by for the maximum date?

excpected result:

8   AA  AA  Z1
1   BB  BB  Z2
10  CC  CC  Z3
3   DD  DD  Z4
5   EE  EE  Z5

Answer 1

This adds an extra column to your output. If you don't want that, you can wrap this query with another select query to select just the fields you want.

SELECT `table 1`.worker_number, `table 1`.first_name, `table 1`.last_name, `table 1`.clinic, max(`table 2`.dt_date) max_dt_date
FROM `health`.`table 1`
LEFT JOIN `health`.`table 2`
       ON `health`.`table 1`.worker_number = `health`.`table 2`.worker_number
group by `table 1`.worker_number, `table 1`.first_name, `table 1`.last_name, `table 1`.clinic
order by max_dt_date desc

Answer 2

You can aggregate on the worker_number and sort on MAX (or MIN based on your needs) of the dt_date :

Try this:

SELECT 
    t1.worker_number, t1.first_name, t1.last_name, t1.clinic
FROM
    `health`.`table 1` t1
        LEFT JOIN
    `health`.`table 2` t2 ON t1.worker_number = t2.worker_number
GROUP BY t1.worker_number
ORDER BY MAX(t2.dt_date) DESC

Answer 3

do the fatc you are not using aggregation function you shoudl need the group by clause but you should use only DISTINCT

SELECT DISTINCT 
      `table 1`.worker_number
    , `table 1`.first_name
    , `table 1`.last_name
    , `table 1`.clinic
FROM `health`.`table 1`
LEFT JOIN `health`.`table 2`
ON `health`.`table 1`.worker_number = `health`.`table 2`.worker_number
order by `health`.`table 2`.dt_date desc

Answer 4

Select worker_number, first_name , last_name , clinic , doctor_type
from table1 t1
where doctor_type = "A"
Order By (Select dt_date from table2
          where worker_number = t1.worker_number 
             and doctor_type = t1.doctor_type)