SQL Help - If Then Else - sql

Question

I need the help of someone who understands SQL better than I do...
I am trying to make a single SP call that uses the IF THEN ELSE but keep getting three "the multi-part identifier could not be bound" messages.
Pages can be sponsored by a Business or a Group.
In the advertEntityType field I have a "B" or a "G" for business or group.
In the advertEntityID field I have the businessID or groupID.
SELECT
Advertisements.advertEntityType
,Advertisements.advertEntityID
FROM Advertisements
WHERE Advertisements.advertPageName = #pageName
IF (Advertisements.advertEntityType = 'G')
SELECT
Group.groupID
,Group.groupName
,Group.groupPhone
,Group.groupWebsite
,Group.groupLogoName
FROM Group
WHERE Group.groupID = Advertisements.advertEntityID
ELSE
SELECT
Business.businessID
,Business.businessName
,Business.businessWorkPhone
,Business.businessWebsite
,Business.businessLogoName
FROM Business
WHERE Business.businessID = Advertisements.advertEntityID
When I try to execute I get these messages which I cannot seem to get my head around...
Msg 4104, Level 16, State 1, Procedure Sponsor_s01, Line 36
The multi-part identifier "Advertisements.advertEntityType" could not be bound.
Msg 4104, Level 16, State 1, Procedure Sponsor_s01, Line 46
The multi-part identifier "Advertisements.advertEntityID" could not be bound.
Msg 4104, Level 16, State 1, Procedure Sponsor_s01, Line 58
The multi-part identifier "Advertisements.advertEntityID" could not be bound.

Answer 1

Advertisements.advertEntityType is a table name and column name. You need to assign these values to local variables if you want to use them in if statements. If I understand correctly you want to evaluate based on the condition in the first select statement. In this case you should use such query:
DECLARE #entityType int --assuming the type of Advertisements.advertEntityType is int
DECLARE #advertEntityID int --assuming the type of Advertisements.advertEntityID is int
SELECT
#entityType = Advertisements.advertEntityType,
#advertEntityID = Advertisements.advertEntityID
FROM Advertisements
WHERE Advertisements.advertPageName = #pageName
IF (#entityType = 'G')
SELECT
Group.groupID
,Group.groupName
,Group.groupPhone
,Group.groupWebsite
,Group.groupLogoName
FROM Group
WHERE Group.groupID = #advertEntityID
ELSE
SELECT
Business.businessID
,Business.businessName
,Business.businessWorkPhone
,Business.businessWebsite
,Business.businessLogoName
FROM Business
WHERE Business.businessID = #advertEntityID