Using parameters of Stored Procedure with Join's "ON" area - tsql

Question

I have parameters like these
declare #Phl1_descr varchar(50)
SET #Phl1_descr = 'Greece'
declare #Phl2_descr varchar(50)
SET #Phl2_descr = 'Coffee & Beverages'
I want to join two tables with the above parameters (if they are not null), so I tried to do something like below in the "ON" keyword of my JOIN
ON
(CASE WHEN LEN(#Phl1_descr) > 0 THEN A.Phl1_descr ELSE B.Phl1_descr END) = B.Phl1_descr AND
(CASE WHEN LEN(#Phl2_descr) > 0 THEN A.Phl2_descr ELSE B.Phl2_descr END) = B.Phl2_descr
However if I send one of the parameters like as '', it doesn't work. Any simpler idea?

Answer 1

Is it posible to use simpler solution? Like:
IF #Phl1_descr IS NOT NULL AND #Phl2_descr IS NOT NULL
BEGIN
SELECT *
FROM Table1 as A
LEFT JOIN Table2 as B on A.Phl1_descr=B.Phl1_descr and A.Phl2_descr=B.Phl2_descr
END
ELSE IF #Phl1_descr IS NOT NULL AND #Phl2_descr IS NULL
BEGIN
SELECT *
FROM Table1 as A
LEFT JOIN Table2 as B on A.Phl1_descr=B.Phl1_descr
END
ELSE IF #Phl1_descr IS NULL AND #Phl2_descr IS NOT NULL
BEGIN
SELECT *
FROM Table1 as A
LEFT JOIN Table2 as B on A.Phl2_descr=B.Phl2_descr
END
So you will get a simpler execution plans and simpler logic.
You can also use ... CASE WHEN #Phl1_descr IS NULL THEN ... to check NULL values

Answer 2

Interesting but
B.Phl1_descr = B.Phl1_descr
not working but
ISNULL(B.Phl1_descr,'-1') = ISNULL(B.Phl1_descr,'-1')
works,
So just a simple change in the below code work it out
(CASE WHEN LEN(#Phl1_descr) > 1 THEN A.Phl1_descr ELSE ISNULL(B.Phl1_descr,'-1') END) = ISNULL(B.Phl1_descr,'-1') AND
(CASE WHEN LEN(#Phl2_descr) > 1 THEN A.Phl2_descr ELSE ISNULL(B.Phl2_descr,'-1') END) = ISNULL(B.Phl2_descr,'-1') AND