Unable to comprehend why a WHERE clause is being accepted [duplicate]

Question

I am trying to understand the difference between HAVING and WHERE. I understand that HAVING is used with GROUP BY statements. However, I cannot understand why the following statement is accepted:

select SUM(child_id) from children WHERE child_ID = 5 GROUP BY Child_ID

Shouldn't the correct statement be select SUM(child_id) from children GROUP BY Child_ID HAVING child_ID = 5 ?

Answer 1

WHERE clauses are executed before the grouping process has occurred, and only have access to fields in the input table. HAVING is performed after the grouping pocess occurs, and can filter results based on the value of aggregate values computed in the grouping process.