Postgres-在從表中選擇值時在INSERT INTO查詢中插入時間戳？

Question

我正在嘗試在Phoenix應用程序中運行遷移，但是Postgrex返回以下錯誤：

null value in column "inserted_at" violates not-null constraint

生成該錯誤的查詢是：

execute "INSERT INTO contract_groups
  (SELECT c.id, fg.group_id FROM contracts c, folder_groups fg
  WHERE c.folder_id = fg.folder_id)"

我嘗試將查詢更新為此：

execute "INSERT INTO contract_groups
  (contract_id, group_id, inserted_at)
  VALUES ((SELECT c.id, fg.group_id FROM contracts c, folder_groups fg 
  WHERE c.folder_id = fg.folder_id), NOW())"

但是我又收到一個錯誤，說subquery must return only one column 。

這是表格的粗略定義。

Answer 1

insert into contract_groups (contract_id, group_id, inserted_at)
select c.id, fg.group_id, CURRENT_TIMESTAMP
from contracts c
inner join folder_groups fg
on fg.folder_id = c.folder_id

請注意，這依賴於與語句中的列順序匹配的所選列

更新：

根據評論，嘗試：

insert into contract_groups (contract_id, group_id, inserted_at)
select distinct c.id, -- distinct added to prevent duplicates
                fg.group_id, 
                CURRENT_TIMESTAMP
from contracts c
inner join folder_groups fg
on fg.folder_id = c.folder_id
where not exists ( -- exclude any combos that are in the target table
                 select 1 
                 from contract_groups cg
                 where cg.contract_id = c.id
                 and fg.froup_id = cg.group_id
                 )