如何在 PostgreSQL 中的“insert select on conflict update”语句中引用 selected 行

Question

这是一个简单的函数，可以将供应库存从一个仓库转移到另一个仓库。它将所有源库存更新到目标仓库，然后从源仓库中删除库存。

这可能是一个愚蠢的语法错误，但我正在努力解析这个函数，因为 on conflict (..) update 子句无法识别 tsrc.stock 并出现错误 ERROR: missing FROM-clause entry for table "tsrc".

create or replace function move_stock_to_another_warehouse (
  _src_warehouse_id int,
  _dst_warehouse_id int,
  _supply_id    int
)
returns int
volatile language sql as $$
  -- try to insert a new row into table warehouse_supply for the destination warehouse
  insert into warehouse_supply as tdst (
    warehouse_id, 
    supply_id,
    stock
  ) 
  select 
    _dst_warehouse_id, 
    _supply_id, 
    stock
  from 
    warehouse_supply as tsrc
  where
    warehouse_id = _src_warehouse_id and 
    supply_id = _supply_id
  on conflict (warehouse_id, supply_id) do update
  -- a row in table warehouse_supply existed for the destination warehouse, just increase the stock
  set
    stock = tdst.stock + tsrc.stock;
    
  -- zero the stocks in the source warehouse
  update
    warehouse_supply as tnew
  set
    stock = 0
  from
    warehouse_supply as told
  where 
    tnew.warehouse_id = _src_warehouse_id and 
    tnew.supply_id = _supply_id and
    told.id = tnew.id
  returning
    coalesce(told.stock, 0); -- returns 0 even if the supply did not exist in the source warehouse
$$;

我尝试了很多方法，甚至使用 with，但找不到让第一个 update 子句知道源数据是 tsrc 的方法。

有什么想法吗？

Answer 1

您可以使用 pseudo-table excluded，其中包含建议插入的行：

...
on conflict (warehouse_id, supply_id) do update
set stock = tdst.stock + excluded.stock

如何在 PostgreSQL 中的“insert select on conflict update”语句中引用 selected 行

How to refer to the selected rows in an `insert select on conflict update` sentence in PostgreSQL

sql

postgresql

sql-update

sql-insert

postgresql-12