-- Phase 3.4: 出站发送记录增加重试相关字段
ALTER TABLE mci_send_record
    ADD COLUMN retry_count INT NOT NULL DEFAULT 0 COMMENT '已重试次数' AFTER send_status,
    ADD COLUMN max_retry INT NOT NULL DEFAULT 0 COMMENT '最大重试次数' AFTER retry_count,
    ADD COLUMN next_retry_time DATETIME NULL COMMENT '下次重试时间' AFTER max_retry;
