SQL Query Not Working

Question

I'm trying to have this query pull all subscribers into a data extension who are not within another data extension. I'm not sure why it's not working.

Select Status, Name, FirstName, LastName, MiddleName, Title, Email, Phone, MobilePhone, Rating, Subscription_Type__c,
Newsletter__c, Marketing_Emails__c, OwnerId, Website, Company, Industry, NumberOfEmployees, LeadSource, Street, City,
PostalCode, State, Country, CreatedById, LastModifiedById, Id 
From Lead_Salesforce 
WHERE LeadSource = 'Sample Request' AND Email NOT IN (
  SELECT Email 
  FROM Contact_Salesforce
)

Answer 1

Email is ambiguous since you're not aliasing anything. Here's how I'd write it:

Select
  l.Status
, l.Name
, l.FirstName
, l.LastName
, l.MiddleName
, l.Title
, l.Email
, l.Phone
, l.MobilePhone
, l.Rating
, l.Subscription_Type__c
, l.Newsletter__c
, l.Marketing_Emails__c
, l.OwnerId
, l.Website
, l.Company
, l.Industry
, l.NumberOfEmployees
, l.LeadSource
, l.Street
, l.City
, l.PostalCode
, l.State
, l.Country
, l.CreatedById
, l.LastModifiedById
, l.Id
From Lead_Salesforce l
WHERE 1=1
and l.LeadSource = 'Sample Request'
and not exists (

  select top 1 c.*
  from Contact_Salesforce c
  where c.email = l.email 

)