I need help with a simple trigger.  I have an object called Media_Plan_History, which is a child to the Opportunity object.  There can only be one active Media Plan History record per Opportunity.

Both objects have a lookup field called Media Planner.  I need a trigger that will fire when the Media Plan History record is updated that would update the Media Planner field on the parent opportunity record to match the Media Planner field on the Media History Plan.

so opp.Media_Planner__c = mph.Media_Planner__c

Here is what I have so far, but I'm missing something important because I keep getting error messages:

trigger OppOwnerSH on Media_Plan_History__c (after update) {

Media_Plan_History__c[] shs;
shs = Trigger.new;

set<Id> oppIds = new Set <ID>();

for (Media_Plan_History__c sh : shs) {
    oppIds.add(sh.Opportunity__c);

Map <ID, Media_Plan_History__c> shforOpps = new Map <ID, Media_Plan_History__c> (
    [select Id, opportunity__c, Media_Planner_2__c, Artist_2__c from Media_Plan_History__c
    where opportunity__c in :oppIds]);

Map<ID, Opportunity> oppsToUpdate = new Map<ID, Opportunity> (
    [select Id, Media_Planner_2__c, Artist_2__c from Opportunity
    where Id in :oppIds]);

for (Opportunity opp : oppsToUpdate) {
    opp.media_planner_2__c = sh.media_planner_2__c;
    update opp;
}}}

Here's the message I'm getting:

I would really appreciate some help with this one.  I'm stil pretty new to coding.  Thank you!!