Join based on variable no of key columns

[vamsi_4a6]

I have table1(master table) consists of four columns(col1,col2,col3,col4).Another table table 2 is present.I have to join these two tables
based on col1,col2,col3 for few records and col1,col2,col3,col4 for few records,col1,col2 for few records.
currently i am using 3 join stages.Is there any way can i
use one join stage instead of three?because my key columns are not constant and it may be 1,2,3,4 columns.

[chulett]

What are your join rules, how do you determine which 'few records' get which combination of keys?

[vamsi_4a6]

1)one set of records
col1='A',col2='B' and col3='C'

for the above set i need to join based on 3 three columns

2)another set of records
col1='D',col2='E'
for the above set i need to join based on 2 columns

3)another set of records

col1='e',col2='f' and col3='g' and col4='h'

for the above set i need to join based on 4 columns

[ray.wurlod]

Basically create a separate join for each circumstance and develop logic to determine which result to use.

[vamsi_4a6]

i do not want to use 4 joins.Just want to know can rewrite the logic some other way

[ray.wurlod]

C'est impossible (pardon my French).

[vinothkumar]

Create a new column where input columns are concatenated based on your joining criteria. (ABC, DE, EFGH). Use that column as key in your JOIN.

[chulett]

Do it in the source SQL... unless, of course, they don't all live together.