Question

I need to join two tables to get all the records from the student_info table and just the records from the student_activities table where the student_id’s are equal.

As there can be multiple records in the student activities table for a single student_id I’m getting duplicates when I print the output using a left join.

SELECT *
FROM student_info 
LEFT JOIN student_activities 
ON student_info.student_id=student_activities.student _id

It was suggested that I use the following but I get errors saying that specific fields are not part of an aggregate function.

SELECT student_info.student_id, student_info.student_name, student_info.phone, student_info.age, COUNT (student_activities.student_id) AS COA
FROM student_info 
LEFT OUTER JOIN student_activities 
ON student_info.student_id=student_activities.student_id 
GROUP BY student_info.student_id

Answer 1

  SELECT student_info.student_id, student_info.student_name, student_info.phone, student_info.age, ISNULL(t.COA, 0) COA
  FROM   student_info
  LEFT   JOIN (SELECT student_id, COUNT(*) COA FROM student_activities GROUP BY student_id) t
  ON     student_info.student_id = t.student_id