Question

I am new to SQL and need a little help with this query:

UPDATE student
SET s.date_of_birth= SELECT count(*) max date_of_birth 
FROM student WHERE batch =st.batch
FROM student s, student st
WHERE st.date_of_birth IS NULL

All i need is to fill date_of_birth where it is empty by counting the most common date_of_birth of that batch. Given what I’ve shown, how can I do this?

Answer 1

Group on the date and sort on the count to get the most common date:

UPDATE s
SET s.date_of_birth = (
  SELECT top 1 date_of_birth
  FROM student
  WHERE batch = s.batch
  GROUP BY date_of_birth
  ORDER BY count(*) desc
)
FROM student s
WHERE s.date_of_birth IS NULL