How to write if exist statement that would run a different select depending if it exists or not - sql

Question

I am trying to convert a sql if exists statement into a SSRS valid format to run a report on CRM.
CRM report doesn't accept the report on upload if I have a if exists method, I'm having troubles figuring out what I can use in its place.
IF EXISTS(select * from dbo.FC where dbo.FC.ContactID in (select dbo.AV.so_contactid from dbo.AV))
begin
select [STATEMENT 1]
from dbo.AV CRMAF_so_AV join
dbo.FC c
on CRMAF_so_AV.so_contactid = c.ContactID;
end
else
begin
select [STATEMENT 2]
from dbo.AV CRMAF_so_AV join
dbo.FA c
on CRMAF_so_AV.so_contactid = c.AccountID;
end;
I want to be able to either run the select [STATEMENT 1] if the condition is true else I want to run select [STATEMENT 2]

Answer 1

I have managed to get this to work by doing a LEFT JOIN instead of a JOIN.
select [STATEMENT 1 + 2 all columns needed]
from dbo.AV CRMAF_so_AV
left join dbo.FC c on CRMAF_so_AV.so_contactid = c.ContactID;
left join dbo.FA a on CRMAF_so_AV.so_contactid = a.AccountID;
This now runs if its an account or a contact.

Answer 2

Try this -
You have to put your entire statement in #select1 and #select1.
declare #statement1 as varchar(max);
declare #statement2 as varchar(max);
SET #statement1 = 'SELECT 1'
SET #statement2 = 'SELECT 2'
IF EXISTS(select * from dbo.FC where dbo.FC.ContactID in (select dbo.AV.so_contactid from dbo.AV))
BEGIN
EXEC (#statement1)
END
ELSE
BEGIN
EXEC (#statement2)
END

Answer 3

Instead of using if exists can you not get a count of records that meet the criteria and then if its 1 or greater run a different query as apposed to if it was equal to 0.
let me know if I am missing something what you are trying to achieve.
sorry i am unable to put comments due to having a new account so my reputation is low.

Answer 4

I think you need something like this:
WITH PreSelection AS (
SELECT
AV.ID AS AVID,
(SELECT TOP(1) c.ContactID FROM dbo.FC c WHERE c.ContactID = AV.so_contactid) AS ContactID,
(SELECT TOP(1) c.ContactID FROM dbo.FA c WHERE c.AccountID = AV.so_contactid) AS AccountID
FROM dbo.AV
)
SELECT
AVID,
ISNULL(
CASE WHEN ContactID IS NULL
THEN (SELECT TOP(1) AccountName FROM dbo.FA WHERE FA.AccountID = AccountID)
ELSE (SELECT TOP(1) LTRIM(RTRIM(ISNULL(FirstName, '') + ' ' + ISNULL(LastName, ''))) FROM dbo.FC WHERE FC.ContactID = ContactID)
END, '') AS ContactName
FROM PreSelection

Answer 5

A few things to note:
When SSRS evaluates query it expects the resluts to always have the same structure in terms of column names and types.
So you CANNOT do something like this..
IF #x=#y
BEGIN
SELECT Name, Age FROM employees
END
ELSE
BEGIN
SELECT DeptID, DeptName, DeptEMpCOunt FROM departments
END
... as this will return different types and column names and column counts.
What you CAN DO is this..
DECLARE #t TABLE(resultType int, colA varchar(128), colB int, colC varchar(128), colD int)
IF #x=#y
BEGIN
INSERT INTO #t(resultType, colA, ColB)
SELECT 1 as resultType, Name, Age FROM employees
END
ELSE
BEGIN
INSERT INTO #t(resultType, colB, colC, colD)
SELECT 2 AS resultType, DeptID, DeptName, DeptEmpCount FROM departments
END
SELECT * FROM #t
Al we are doing is creating a table that can handle all variations of the data and putting the results into whatever columns can accommodate that data type.
This will always return the same data structure so SSRS will be happy, then you will need to handle which columns to display your data from based on what gets returned, hence why I added the result type to the results so you can test that from within the report.