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;
