[SQL 배우기] Section 3. GROUP BY Statements

Aggregate function: take multiple inputs and return a single output

• AVG(), COUNT(), MAX(), MIN(), SUM()
• can only happen in the SELECT or HAVING clause
• ordering result of the aggregate function requires ORDER BY reference to the entire function

 

GROUP BY: allows for the aggregation of columns by some category

• must appear right after a FROM or WHERE statement
• you can use an aggregate function with it
• in the SELECT statement, columns must either have an aggregate function or be in the GROUP BY call
• WHERE statement should not refer to the aggregation result

 

HAVING: allows for filtering after aggregation

• WHERE cannot be used to filter based on aggregated results