mysql 查询拆分

在 MySQL 数据库中，查询拆分是一种优化技术，它将一个复杂的查询拆分成多个简单的查询，然后将结果组合在一起，以提高查询性能。以下是一些关于 MySQL 查询拆分的示例和说明。

/* 示例 1：将一个复杂查询拆分成两个简单查询 */ -- 第一个查询 SELECT customer_id, SUM(amount) AS total_spent FROM orders GROUP BY customer_id HAVING total_spent >1000; -- 第二个查询 SELECT customer_id, AVG(amount) AS average_spent FROM orders GROUP BY customer_id HAVING average_spent1000; -- 第二个查询 SELECT customer_id, COUNT(*) AS num_orders FROM orders GROUP BY customer_id HAVING num_orders >3; -- 使用 UNION ALL 组合两个查询的结果 SELECT customer_id, total_spent, num_orders FROM ( SELECT customer_id, SUM(amount) AS total_spent, NULL AS num_orders FROM orders GROUP BY customer_id HAVING total_spent >1000 UNION ALL SELECT customer_id, NULL AS total_spent, COUNT(*) AS num_orders FROM orders GROUP BY customer_id HAVING num_orders >3 ) AS intermediate_table;