如何将值从一列连接到另一列

Question

I have two tables Notification and Worker Notifications. On those tables there are two similar columns called Time. My worker class inherits Notification and I would like to join all preexisting times on worker with notification time.

id | Worker| Time
-------------
10 | John| 8/17/2019
20 | Rui| 8/17/2019
30 | Pen| 8/17/2019

id | Notification| Time |WorkerID
-----------------------------------
10 | John| 8/17/2019 | 10
20 | Rui| 8/17/2019  |20
30 | Pen| 8/17/2019  |30

SELECT category_id, col1, col2, col3 FROM items_a UNION SELECT category_id, col1, col2, col3 FROM items_b

Answer 1

I dare say it should actually be

SELECT *
FROM 
  worker w 
  INNER JOIN
  notifications n
  ON 
    w.id = n.workerid

I say this because a notification has a workerid so it clearly "belongs to a worker" - it isn't necessarily related to a worker based on the time, as if two times are the same then you could end up joining a notification assigned to John, to Dave intead

But if you insist on joining on the time the pattern is the same:

SELECT *
FROM 
  worker w 
  INNER JOIN
  notifications n
  ON 
    w.time = n.time 

JOIN causes your result set to grow sideways (more columns). UNION causes your result set to grow vertically (more rows)