How to extract dataset from two tables with different time parameters?

Question

SQL

Hello.
Prompt or suggest an idea, please, who knows.
Given :
table 1 of the form:

datetime	param1
2018-08-01 12:10	red
2018-08-02 15:20	green
2018-08-03 08:30	blue

table 2 types:

datetime	param2
2018-08-01 12:15	123
2018-08-01 13:20	234
2018-08-01 22:30	345
2018-08-02 16:10	456
2018-08-02 21:15	567

The value of parameter 1 changes once a day. The value of parameter 2 changes thousands of times a day.
Required to get :

datetime	param2	param1
2018-08-01 12:15	123	red
2018-08-01 13:20	234	red
2018-08-01 22:30	345	red
2018-08-02 16:10	456	green
2018-08-02 21:15	567	green

Those. a data set with the values ​​of date-time and parameter 2 from table 2 and the current value of parameter 1 from table 1.
Is it possible to get this with one fast enough sql query?
Thank you.

Answer 1

Hmm... For oracle, I would get out like this:

SELECT  
t2.datetime
, param2
, (SELECT param1 
  FROM
     (SELECT 
         t1.param1 
      ,  row_number() OVER(ORDER BY t1.datetime DESC)  rankparam1
      FROM table1 t1  
      WHERE t2.datetime>=t1.datetime)  
   WHERE rankparam1 = 1)
  as param1
FROM table2  t2

I believe in others the base is about the same.
But I'm not sure that it will be fast enough (even if you place the indexes correctly).