diff --git a/supabase-schema.sql b/supabase-schema.sql
index 9b004ed..8791908 100644
--- a/supabase-schema.sql
+++ b/supabase-schema.sql
@@ -1,70 +1,101 @@
+-- ============================================================
 -- CampGear Supabase Schema
--- Run this in Supabase SQL Editor
+-- Supabase SQL Editor에서 실행
+-- 멱등성 보장: 재실행해도 안전 (IF NOT EXISTS / DO 블록 사용)
+-- ============================================================
 
--- Enable UUID extension
+-- UUID 확장
 CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
 
--- ENUM types
-CREATE TYPE equipment_category AS ENUM (
-  'tent', 'sleeping', 'cooking', 'lighting', 'clothing',
-  'backpack', 'furniture', 'safety', 'electronics', 'other'
-);
 
-CREATE TYPE sale_status AS ENUM ('listing', 'reserved', 'sold', 'cancelled');
-CREATE TYPE sale_platform AS ENUM ('danggeun', 'bunjang', 'joonggo', 'naver', 'other');
+-- ============================================================
+-- ENUM 타입 (이미 존재하면 무시)
+-- ============================================================
 
--- purchases table
-CREATE TABLE purchases (
-  id UUID DEFAULT uuid_generate_v4() PRIMARY KEY,
-  user_id UUID REFERENCES auth.users(id) ON DELETE CASCADE NOT NULL,
-  name TEXT NOT NULL,
-  category equipment_category NOT NULL,
-  brand TEXT,
-  price INTEGER NOT NULL DEFAULT 0,
-  purchase_date DATE NOT NULL,
-  store TEXT,
+DO $$ BEGIN
+  CREATE TYPE equipment_category AS ENUM (
+    'tent', 'sleeping', 'cooking', 'lighting', 'clothing',
+    'backpack', 'furniture', 'safety', 'electronics', 'other'
+  );
+EXCEPTION WHEN duplicate_object THEN NULL;
+END $$;
+
+DO $$ BEGIN
+  CREATE TYPE sale_status AS ENUM ('listing', 'reserved', 'sold', 'cancelled');
+EXCEPTION WHEN duplicate_object THEN NULL;
+END $$;
+
+DO $$ BEGIN
+  CREATE TYPE sale_platform AS ENUM ('danggeun', 'bunjang', 'joonggo', 'naver', 'other');
+EXCEPTION WHEN duplicate_object THEN NULL;
+END $$;
+
+
+-- ============================================================
+-- 테이블
+-- ============================================================
+
+CREATE TABLE IF NOT EXISTS purchases (
+  id            UUID         DEFAULT uuid_generate_v4() PRIMARY KEY,
+  user_id       UUID         REFERENCES auth.users(id) ON DELETE CASCADE NOT NULL,
+  name          TEXT         NOT NULL,
+  category      equipment_category NOT NULL,
+  brand         TEXT,
+  price         INTEGER      NOT NULL DEFAULT 0,
+  quantity      INTEGER      NOT NULL DEFAULT 1,
+  purchase_date DATE         NOT NULL,
+  store         TEXT,
   warranty_until DATE,
-  notes TEXT,
-  created_at TIMESTAMPTZ DEFAULT NOW() NOT NULL,
-  updated_at TIMESTAMPTZ DEFAULT NOW() NOT NULL
+  notes         TEXT,
+  created_at    TIMESTAMPTZ  DEFAULT NOW() NOT NULL,
+  updated_at    TIMESTAMPTZ  DEFAULT NOW() NOT NULL
 );
 
--- used_sales table
-CREATE TABLE used_sales (
-  id UUID DEFAULT uuid_generate_v4() PRIMARY KEY,
-  user_id UUID REFERENCES auth.users(id) ON DELETE CASCADE NOT NULL,
-  purchase_id UUID REFERENCES purchases(id) ON DELETE SET NULL,
-  item_name TEXT NOT NULL,
-  sale_price INTEGER NOT NULL DEFAULT 0,
+CREATE TABLE IF NOT EXISTS used_sales (
+  id          UUID        DEFAULT uuid_generate_v4() PRIMARY KEY,
+  user_id     UUID        REFERENCES auth.users(id) ON DELETE CASCADE NOT NULL,
+  purchase_id UUID        REFERENCES purchases(id) ON DELETE SET NULL,
+  item_name   TEXT        NOT NULL,
+  sale_price  INTEGER     NOT NULL DEFAULT 0,
   final_price INTEGER,
-  platform sale_platform NOT NULL,
-  status sale_status NOT NULL DEFAULT 'listing',
-  notes TEXT,
-  listed_at DATE NOT NULL,
-  sold_at DATE,
+  platform    sale_platform NOT NULL,
+  status      sale_status   NOT NULL DEFAULT 'listing',
+  notes       TEXT,
+  listed_at   DATE        NOT NULL,
+  sold_at     DATE,
+  created_at  TIMESTAMPTZ DEFAULT NOW() NOT NULL,
+  updated_at  TIMESTAMPTZ DEFAULT NOW() NOT NULL
+);
+
+CREATE TABLE IF NOT EXISTS ai_conversations (
+  id         UUID        DEFAULT uuid_generate_v4() PRIMARY KEY,
+  user_id    UUID        REFERENCES auth.users(id) ON DELETE CASCADE NOT NULL,
+  title      TEXT        NOT NULL DEFAULT '새 대화',
   created_at TIMESTAMPTZ DEFAULT NOW() NOT NULL,
   updated_at TIMESTAMPTZ DEFAULT NOW() NOT NULL
 );
 
--- ai_conversations table
-CREATE TABLE ai_conversations (
-  id UUID DEFAULT uuid_generate_v4() PRIMARY KEY,
-  user_id UUID REFERENCES auth.users(id) ON DELETE CASCADE NOT NULL,
-  title TEXT NOT NULL DEFAULT '새 대화',
-  created_at TIMESTAMPTZ DEFAULT NOW() NOT NULL,
-  updated_at TIMESTAMPTZ DEFAULT NOW() NOT NULL
+CREATE TABLE IF NOT EXISTS ai_messages (
+  id              UUID        DEFAULT uuid_generate_v4() PRIMARY KEY,
+  conversation_id UUID        REFERENCES ai_conversations(id) ON DELETE CASCADE NOT NULL,
+  role            TEXT        NOT NULL CHECK (role IN ('user', 'assistant')),
+  content         TEXT        NOT NULL,
+  created_at      TIMESTAMPTZ DEFAULT NOW() NOT NULL
 );
 
--- ai_messages table
-CREATE TABLE ai_messages (
-  id UUID DEFAULT uuid_generate_v4() PRIMARY KEY,
-  conversation_id UUID REFERENCES ai_conversations(id) ON DELETE CASCADE NOT NULL,
-  role TEXT NOT NULL CHECK (role IN ('user', 'assistant')),
-  content TEXT NOT NULL,
-  created_at TIMESTAMPTZ DEFAULT NOW() NOT NULL
-);
 
--- updated_at trigger function
+-- ============================================================
+-- 컬럼 마이그레이션 (ADD COLUMN IF NOT EXISTS)
+-- ============================================================
+
+-- purchases.quantity 추가 (기존 테이블에 없을 경우)
+ALTER TABLE purchases ADD COLUMN IF NOT EXISTS quantity INTEGER NOT NULL DEFAULT 1;
+
+
+-- ============================================================
+-- updated_at 자동 갱신 트리거
+-- ============================================================
+
 CREATE OR REPLACE FUNCTION update_updated_at()
 RETURNS TRIGGER AS $$
 BEGIN
@@ -73,35 +104,48 @@ BEGIN
 END;
 $$ LANGUAGE plpgsql;
 
--- Apply triggers
-CREATE TRIGGER purchases_updated_at BEFORE UPDATE ON purchases
+DROP TRIGGER IF EXISTS purchases_updated_at ON purchases;
+CREATE TRIGGER purchases_updated_at
+  BEFORE UPDATE ON purchases
   FOR EACH ROW EXECUTE FUNCTION update_updated_at();
 
-CREATE TRIGGER used_sales_updated_at BEFORE UPDATE ON used_sales
+DROP TRIGGER IF EXISTS used_sales_updated_at ON used_sales;
+CREATE TRIGGER used_sales_updated_at
+  BEFORE UPDATE ON used_sales
   FOR EACH ROW EXECUTE FUNCTION update_updated_at();
 
-CREATE TRIGGER ai_conversations_updated_at BEFORE UPDATE ON ai_conversations
+DROP TRIGGER IF EXISTS ai_conversations_updated_at ON ai_conversations;
+CREATE TRIGGER ai_conversations_updated_at
+  BEFORE UPDATE ON ai_conversations
   FOR EACH ROW EXECUTE FUNCTION update_updated_at();
 
+
+-- ============================================================
 -- Row Level Security
-ALTER TABLE purchases ENABLE ROW LEVEL SECURITY;
-ALTER TABLE used_sales ENABLE ROW LEVEL SECURITY;
-ALTER TABLE ai_conversations ENABLE ROW LEVEL SECURITY;
-ALTER TABLE ai_messages ENABLE ROW LEVEL SECURITY;
+-- ============================================================
 
--- RLS Policies: purchases
+ALTER TABLE purchases       ENABLE ROW LEVEL SECURITY;
+ALTER TABLE used_sales      ENABLE ROW LEVEL SECURITY;
+ALTER TABLE ai_conversations ENABLE ROW LEVEL SECURITY;
+ALTER TABLE ai_messages     ENABLE ROW LEVEL SECURITY;
+
+-- purchases RLS
+DROP POLICY IF EXISTS "Users can manage own purchases" ON purchases;
 CREATE POLICY "Users can manage own purchases" ON purchases
   FOR ALL USING (auth.uid() = user_id);
 
--- RLS Policies: used_sales
+-- used_sales RLS
+DROP POLICY IF EXISTS "Users can manage own used_sales" ON used_sales;
 CREATE POLICY "Users can manage own used_sales" ON used_sales
   FOR ALL USING (auth.uid() = user_id);
 
--- RLS Policies: ai_conversations
+-- ai_conversations RLS
+DROP POLICY IF EXISTS "Users can manage own conversations" ON ai_conversations;
 CREATE POLICY "Users can manage own conversations" ON ai_conversations
   FOR ALL USING (auth.uid() = user_id);
 
--- RLS Policies: ai_messages (via conversation ownership)
+-- ai_messages RLS (대화 소유자를 통해 접근)
+DROP POLICY IF EXISTS "Users can manage messages in own conversations" ON ai_messages;
 CREATE POLICY "Users can manage messages in own conversations" ON ai_messages
   FOR ALL USING (
     conversation_id IN (