Postgres-在从表中选择值时在INSERT INTO查询中插入时间戳？

Question

我正在尝试在Phoenix应用程序中运行迁移，但是Postgrex返回以下错误：

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

生成该错误的查询是：

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

我尝试将查询更新为此：

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())"

但是我又收到一个错误，说subquery must return only one column 。

这是表格的粗略定义。

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

请注意，这依赖于与语句中的列顺序匹配的所选列

更新：

根据评论，尝试：

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
                 )