优化一下上面的语句

这段 SQL 查询语句可以进行以下优化：

1. 使用 JOIN ON 代替嵌套查询：嵌套查询会增加查询的复杂度和执行时间，而使用 JOIN ON 可以将查询合并为一条语句，提高查询效率。修改后的 SQL 查询语句如下：

SELECT d.*, IFNULL(SUM(e.`unit_price` * e.num), 0) AS total_price,
    IF(COUNT(*) * 3 = SUM(IF(e.in_storage_amount > 0, IF(e.in_storage_amount >= e.num, 2, 1), 0)), 3,
        IF(SUM(IF(e.in_storage_amount > 0, IF(e.in_storage_amount >= e.num, 2, 1), 0)) > 0, 1, 0)) AS in_storage_status,
    IF(e.id IS NULL, 0, COUNT(*)) AS record_count
FROM USER b
JOIN `order` c ON c.user_id = b.id AND c.id IN (<foreach collection="orderIds" item="item" index="index" separator=" , " open="(" close=")">#{item}</foreach>)
LEFT JOIN order_record e ON d.id = e.`order_id` AND e.`delete_flag` = 0
GROUP BY d.id
ORDER BY d.create_time DESC

2. 避免使用 IF 函数：IF 函数在执行时会进行逻辑判断和计算，会增加查询的复杂度和执行时间，而使用 CASE WHEN 可以避免 IF 函数的使用，提高查询效率。修改后的 SQL 查询语句如下：

SELECT d.*, IFNULL(SUM(e.`unit_price` * e.num), 0) AS total_price,
    CASE WHEN COUNT(*) * 3 = SUM(CASE WHEN e.in_storage_amount > 0 THEN CASE WHEN e.in_storage_amount >= e.num THEN 2 ELSE 1 END ELSE 0 END) THEN 3
        WHEN SUM(CASE WHEN e.in_storage_amount > 0 THEN CASE WHEN e.in_storage_amount >= e.num THEN 2 ELSE 1 END ELSE 0 END) > 0 THEN 1
        ELSE 0 END AS in_storage_status,
    IF(e.id IS NULL, 0, COUNT(*)) AS record_count
FROM USER b
JOIN `order` c ON c.user_id = b.id AND c.id IN (<foreach collection="orderIds" item="item" index="index" separator=" , " open="(" close=")">#{item}</foreach>)
LEFT JOIN order_record e ON d.id = e.`order_id` AND e.`delete_flag` = 0
GROUP BY d.id
ORDER BY d.create_time DESC

3. 使用连接池：在高并发的情况下，频繁地创建和释放数据库连接会增加系统的负担，而使用连接池可以复用数据库连接，避免频繁地创建和释放数据库连接，提高系统的性能和稳定性。