帮买帮取帮送怎样分业务？表单约束与报价版本设计

CREATE TABLE errand_draft (
 id text PRIMARY KEY,
 revision bigint NOT NULL CHECK (revision > 0),
 kind text NOT NULL CHECK (kind IN ('buy','pickup','send')),
 destination text NOT NULL CHECK (length(trim(destination)) > 0),
 pickup text,
 shop text,
 goods text,
 budget_cents bigint,
 item text,
 state text NOT NULL CHECK (state IN ('editing','confirmed','submitted')),
 CHECK (
  (kind='buy' AND shop IS NOT NULL AND length(trim(shop))>0
   AND goods IS NOT NULL AND length(trim(goods))>0 AND budget_cents>0
   AND pickup IS NULL AND item IS NULL)
  OR
  (kind IN ('pickup','send') AND pickup IS NOT NULL
   AND length(trim(pickup))>0 AND item IS NOT NULL
   AND length(trim(item))>0 AND shop IS NULL AND goods IS NULL
   AND budget_cents IS NULL)
 ),
 CHECK (kind <> 'buy' OR budget_cents IS NOT NULL)
);
CREATE TABLE quote (
 id text PRIMARY KEY,
 draft_id text NOT NULL REFERENCES errand_draft(id),
 draft_revision bigint NOT NULL CHECK (draft_revision > 0),
 service_cents bigint NOT NULL CHECK (service_cents >= 0),
 expires_at timestamptz NOT NULL
);

BEGIN;
SELECT revision,state FROM errand_draft WHERE id=$1 FOR UPDATE;
SELECT draft_id,draft_revision,expires_at FROM quote WHERE id=$2 FOR UPDATE;
-- 应用核对归属、当前revision、confirmed状态与有效期；不符ROLLBACK。
-- 核对通过后，再以同一事务插入唯一请求标识对应的订单并修改状态。
UPDATE errand_draft SET state='submitted'
 WHERE id=$1 AND revision=$3 AND state='confirmed';
-- 必须检查受影响行数等于1，否则ROLLBACK，不能无条件提交。
COMMIT;