大多数WHERE子句都可以用HAVING来替代。唯一的差别是,WHERE过滤行,而HAVING过滤分组,
WHERE在数据分组前进行过滤,HAVING在数据分组后进行过滤
SELECT vend_id, COUNT(*) AS num_prods
FROM Products
WHERE prod_price >= 4
GROUP BY vend_id
HAVING COUNT(*) >= 2;
大多数WHERE子句都可以用HAVING来替代。唯一的差别是,WHERE过滤行,而HAVING过滤分组,
WHERE在数据分组前进行过滤,HAVING在数据分组后进行过滤
SELECT vend_id, COUNT(*) AS num_prods
FROM Products
WHERE prod_price >= 4
GROUP BY vend_id
HAVING COUNT(*) >= 2;