Question

I would like to use a table alias within the projection of another select statement, like this:

SELECT [ID]
      ,[Name]
      ,CASE WHEN 'reptile' IN 
      (SELECT [Type] FROM dbo.Pets [S] INNER JOIN [P] ON S.People_ID = P.ID) 
      THEN 1 ELSE 0 END [HasReptile]
  FROM People [P]

Within the projection there is a select statement, which is trying to use the table alias [P]. Evidentally this is not legal. How can I achieve my goal without using two separate queries?

In effect, my query is saying “show ‘1’ for any person who owns a pet of type ‘reptile’.

I am using SQL Server 2008.

Answer 1

SELECT [ID]
      ,[Name]
      ,CASE WHEN 'reptile' IN 
      (SELECT [Type] FROM dbo.Pets [S] WHERE S.People_ID = P.ID) 
      THEN 1 ELSE 0 END [HasReptile]
  FROM People [P]