优化：按商户分组展示员工账号

backend/internal/service/user.go

@@ -28,6 +28,15 @@ type UserListQuery struct {
 	Status     *int
 }
 
+// MerchantMemberGroup keeps employee assignments grouped by merchant for
+// platform account management. Pagination is intentionally based on merchants
+// so one merchant's employees are never split across pages.
+type MerchantMemberGroup struct {
+	MerchantID uint                   `json:"merchant_id"`
+	Merchant   *model.Merchant        `json:"merchant,omitempty"`
+	Members    []model.MerchantMember `json:"members"`
+}
+
 func (s *UserService) List(q UserListQuery) ([]model.User, int64, error) {
 	if q.Page < 1 {
 		q.Page = 1
@@ -59,21 +68,51 @@ func (s *UserService) List(q UserListQuery) ([]model.User, int64, error) {
 	return list, total, err
 }
 
-// ListMerchantMembers returns employee assignments across merchants for platform operations.
-func (s *UserService) ListMerchantMembers(page, size int) ([]model.MerchantMember, int64, error) {
+// ListMerchantMembers returns employee assignments grouped by merchant for platform operations.
+func (s *UserService) ListMerchantMembers(page, size int) ([]MerchantMemberGroup, int64, error) {
 	page, size = normalizePage(page, size)
 	tx := s.db.Model(&model.MerchantMember{}).
 		Joins("JOIN users ON users.id = merchant_members.user_id AND users.deleted_at IS NULL").
 		Where("users.role = ?", model.RoleMerchant)
 	var total int64
-	if err := tx.Count(&total).Error; err != nil {
+	if err := tx.Distinct("merchant_members.merchant_id").Count(&total).Error; err != nil {
 		return nil, 0, err
 	}
+	var merchantIDs []uint
+	if err := tx.Distinct("merchant_members.merchant_id").
+		Order("merchant_members.merchant_id ASC").
+		Offset((page-1)*size).Limit(size).Pluck("merchant_members.merchant_id", &merchantIDs).Error; err != nil {
+		return nil, 0, err
+	}
+	if len(merchantIDs) == 0 {
+		return []MerchantMemberGroup{}, total, nil
+	}
 	var members []model.MerchantMember
-	err := tx.Preload("Merchant").Preload("User").
+	err := s.db.Model(&model.MerchantMember{}).
+		Joins("JOIN users ON users.id = merchant_members.user_id AND users.deleted_at IS NULL").
+		Where("users.role = ? AND merchant_members.merchant_id IN ?", model.RoleMerchant, merchantIDs).
+		Preload("Merchant").Preload("User").
 		Order("merchant_members.merchant_id ASC, merchant_members.id ASC").
-		Offset((page - 1) * size).Limit(size).Find(&members).Error
-	return members, total, err
+		Find(&members).Error
+	if err != nil {
+		return nil, 0, err
+	}
+
+	groupsByMerchant := make(map[uint]*MerchantMemberGroup, len(merchantIDs))
+	groups := make([]MerchantMemberGroup, 0, len(merchantIDs))
+	for _, merchantID := range merchantIDs {
+		group := MerchantMemberGroup{MerchantID: merchantID, Members: []model.MerchantMember{}}
+		groups = append(groups, group)
+		groupsByMerchant[merchantID] = &groups[len(groups)-1]
+	}
+	for _, member := range members {
+		group := groupsByMerchant[member.MerchantID]
+		if group.Merchant == nil {
+			group.Merchant = member.Merchant
+		}
+		group.Members = append(group.Members, member)
+	}
+	return groups, total, nil
 }
 
 func (s *UserService) Create(username, password, nickname, role string, merchantID uint) (*model.User, error) {