Mysql exercise ---- SUM and COUNT/zh figure (2 ),

Mysql exercise ---- SUM and COUNT/zh figure (2 ),
World country overview

GROUPAndHAVING

By includingGROUPSub-statement function,SUMAnd setCOUNTIt is applied to the project group with shared values. When you specifyGroup by continentThe result is that only one row is obtained for each different value.Continent. All other columns must be "aggregated" bySUM,COUNT...

TheHAVINGClause allows you to filter display groups. TheWHEREThe clause filters rows before aggregation.HAVINGFilter clauses after aggregation.

IfORDERContains a clause. We can reference columns by their positions.