SQL Query: How to send MIN value from one table to another based off ID

Question

Looking for help with SQL query!

I have 2 tables, A and B. Both tables have the column 'student_id' and 'created_date'. For table A, 'created_date' is null but I wish to populate it with data from table B.

In table B, there are multiple of the same 'student_id' values, so I am trying to fetch only the one that has the earliest 'created_date'.

Once I get that date, I want to then go back to table A, look for that exact same 'student_id' and then insert that MIN 'created_date' into table A.

If anybody could help that would be greatly appreciated!

UPDATE student as A 
INNER JOIN (SELECT MIN(student_registration.created_date) mindate, student_id FROM student_registration GROUP By student_id ) B 
ON A.student_id = B.student_id 
SET A.`created_date` = B.mindate 
WHERE A.`created_date` is null;

Answer 1

You can make something like this

Update Tablea A 
inner join (SELECT MIN(`created_date`) mindate, student_id 
FROM Tableb 
GROUP By student_id ) B 
On A.student_id = B.student_id 
Set A.`created_date` = B.mindate 
Where A.`created_date` is NULL ;

With the inner join you find the minimal Date in TableB and it is the right one for the student_id.

The rest is simple Updatelogic.

With the Where Clause at the end you can select only the rows that you need.

For Postgresql is the query like this

UPDATE student as A 
SET created_date = B.mindate 
FROM (Select MIN(created_date) as mindate, student_id 
From student_registration 
  GROUP BY student_id)
as B
WHERE A.student_id = B.student_id 
AND A.created_date is null;