-- 20261009 商户投递记录分页索引（可重复执行）
--
-- 背景：/app-message/pc/deliveries 页面查询（source_mch_id + recipient_user_id 过滤，
--       create_time desc, id desc 排序）在 third_push_delivery 上仅有
--       (tenant_id, source_mch_id, create_time, del_flag) 索引，recipient_user_id
--       不在索引中，需沿商户范围逐行回表过滤；表增长到约 21 万行后实测 COUNT 约 2.2 秒。
-- 方案：新增与页面查询形态精确匹配的复合索引，等值(mch, recipient)后按 create_time 有序，
--       分页与 COUNT 均为索引前缀范围扫描；无 recipient 条件时退回既有商户时间索引，不受影响。
-- 执行：Online DDL（INPLACE + LOCK=NONE，不锁表），21 万行预计 5~15 秒，建议低峰执行。
-- 回滚：文末 DROP INDEX。

USE pjcloudx_thirdparty;
SET @ddl = IF(
    (SELECT COUNT(*) FROM information_schema.statistics
     WHERE table_schema = 'pjcloudx_thirdparty' AND table_name = 'third_push_delivery'
       AND index_name = 'idx_third_push_delivery_mch_recipient') = 0,
    'ALTER TABLE third_push_delivery ADD INDEX idx_third_push_delivery_mch_recipient (tenant_id, source_mch_id, recipient_user_id, create_time, id), ALGORITHM=INPLACE, LOCK=NONE',
    'SELECT ''skip: idx_third_push_delivery_mch_recipient 已存在'' AS msg');
PREPARE stmt FROM @ddl;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
ANALYZE TABLE third_push_delivery;

-- ============ 执行后验证（期望 key=idx_third_push_delivery_mch_recipient） ============
-- EXPLAIN SELECT id FROM pjcloudx_thirdparty.third_push_delivery
--  WHERE tenant_id = 1 AND source_mch_id = 2078051759222632449
--    AND recipient_user_id = 2034824566572941314
--  ORDER BY create_time DESC, id DESC LIMIT 20;

-- ============ 回滚（如需） ============
-- ALTER TABLE pjcloudx_thirdparty.third_push_delivery DROP INDEX idx_third_push_delivery_mch_recipient;