HAVE 是 SQL 中的一个子句,通常与 GROUP BY 和聚合函数一起使用,用于过滤分组后的结果
以下是一些关于如何正确使用 HAVING 语句的示例:
SELECT column_name(s), aggregate_function(column_name)
FROM table_name
GROUP BY column_name(s)
HAVING condition;
假设我们有一个名为 “orders” 的表格,包含以下列:customer_id、order_date 和 amount。我们想要查询每个客户的总金额,并且只显示总金额大于 1000 的客户。
SELECT customer_id, SUM(amount) as total_amount
FROM orders
GROUP BY customer_id
HAVING total_amount > 1000;
如果你想根据多个条件对分组后的结果进行过滤,可以在 HAVING 子句中使用 AND、OR 或 NOT 连接条件。
SELECT customer_id, SUM(amount) as total_amount, COUNT(*) as total_orders
FROM orders
GROUP BY customer_id
HAVING total_amount > 1000 AND total_orders > 5;
你还可以在 HAVING 子句中使用聚合函数,例如 AVG(), COUNT(), MAX(), MIN() 等。
SELECT customer_id, AVG(amount) as average_amount
FROM orders
GROUP BY customer_id
HAVING AVG(amount) > 100;
总之,HAVING 子句用于过滤分组后的结果,它通常与 GROUP BY 和聚合函数一起使用。请确保在使用 HAVING 时正确地指定分组列和条件。