SELECT vend_id, COUNT(*) AS num_prods FROM products #GROUP BY子句可以包含任意数目的列，多行NULL值将分为一组GROUP BY vend_id; #GROUP BY子句必须出现在WHERE子句之后，ORDER BY子句之前。SELECT cust_id, COUNT(*) AS orders FROM orders #Having非常类似于Where，都是起过滤作用，唯一的差别是GROUP BY cust_id HAVING COUNT(*) >= 2; #Where过滤行，Having过滤分组。SELECT vend_id, COUNT(*) AS num_prods FROM products WHERE prod_price >= 10GROUP BY vend_idHAVING COUNT(*) >= 2;SELECT order_num, SUM(quantity*item_price) AS ordertotal FROM orderitemsGROUP BY order_numHAVING SUM(quantity*item_price) >= 50ORDER BY ordertotal; #Group by的输出可能不是分组的顺序

Select子句及其顺序