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backend/migrations/012_add_user_subscription_soft_delete.sql

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+-- 012: 为 user_subscriptions 表添加软删除支持
+-- 任务：fix-medium-data-hygiene 1.1
+
+-- 添加 deleted_at 字段
+ALTER TABLE user_subscriptions
+ADD COLUMN IF NOT EXISTS deleted_at TIMESTAMPTZ DEFAULT NULL;
+
+-- 添加 deleted_at 索引以优化软删除查询
+CREATE INDEX IF NOT EXISTS usersubscription_deleted_at
+ON user_subscriptions (deleted_at);
+
+-- 注释：与其他使用软删除的实体保持一致
+COMMENT ON COLUMN user_subscriptions.deleted_at IS '软删除时间戳，NULL 表示未删除';