学习 SQL 语句 - Select(8): 分组条件

代码文件:
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//分组条件可以是 Where
procedure TForm1.Button1Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT Continent, AVG(Area) AS 平均面积 ' +
'FROM country WHERE Continent="South America" GROUP BY Continent';
Open;
end;
end;

//也可以是 Having
procedure TForm1.Button2Click(Sender: TObject);
begin
with ADODataSet1 do begin
Close;
CommandText := 'SELECT Continent, AVG(Area) AS 平均面积 ' +
'FROM country GROUP BY Continent HAVING Continent<>"South America"';
Open;
end;
end;