help required in writing a query

hi all,

consider the following scenario:

I have 2 tables ModelSalesUnitCode and SalesUnitCode with following data:

ModelSalesUnit
Kis Type Salu_cd
PC 6 2AA01
WA 3 2AA01
Wa 3 3AA01

SalesUnitCode
Salu_cd Kis Type Salu_desc
2AA01 null null generic description
2AA01 WA 3 WA description
3AA01 WA 3 generic description

Now I write this query to get the salu_cd and their respective descriptions for the model with (kis = WA and Type = 3)

Select
a.kis,
a.type,
a.salu_cd,
b.salu_desc
From
modelsalesunitcode a, salesunitcode b
Where
b.salu_cd = a.salu_cd
And
a.kis = 'WA'
And
a.type = '3'

This gives me
kis type salu_cd salu_desc
WA 3 2AA01 generic description
WA 3 2AA01 WA description
WA 3 3AA01 generic description

is it possible to modify the above query in such a way that it returns

kis type salu_cd salu_desc
WA 3 2AA01 WA description
WA 3 3AA01 generic description

meaning where description exists for (Kis = WA and Type = 3) pick it up (WA Description in above case) if it does not exist then pick the generic description.

Thanx in advance
Omer

/Add clause in WHERE:

Select
a.kis,
a.type,
a.salu_cd,
b.salu_desc
From
modelsalesunitcode a, salesunitcode b
Where
b.salu_cd = a.salu_cd
And
a.kis = 'WA'
And
a.type = '3'
--------
AND b.kis IS NOT NULL
--------