Postgres 删除前触发检查金额 [英] Postgres trigger check amount before delete

问题描述

我正在尝试在触发器之前创建一个 postgres，以检查在实际删除之前将要删除的记录数量.例如不删除超过 5 条记录

I am trying to create a postgres before trigger to check the amount of records that are going to be deleted before it actually does. For example to not delete more than 5 records

推荐答案

您可以使用 AFTER DELETE 语句级触发器来实现这一点.在触发器函数中，您可以计算受影响的行数，如果计数过高则抛出异常.该异常将强制回滚发起删除的事务.

You could achieve that with an AFTER DELETE statement-level trigger. Inside the trigger function you can count the number of affected rows and throw an exception if the count is too high. The exception will force a rollback of the transaction that initiated the delete.

create function prevent_delete()
  returns trigger
as
$BODY$ 
declare
  l_count integer;
begin 
  select count(*)
    into l_count
  from old_table;

  if l_count > 5 then 
    raise exception 'Too many rows would be deleted';
  end if; 
  return null;
end; 
$BODY$ 
LANGUAGE plpgsql;

然后创建触发器:

create trigger prevent_mass_delete 
   after delete on the_table
   referencing old table as old_table
   for each statement 
   execute procedure prevent_delete();

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