Two types 
One - to -one mergeing:
combine observations from two data sets into a single 
observation in a new data set: 

Match- Merging:combine observations from two data sets into 
a single observation in a new data set according to the 
values of a variable that is specified in the BY statement:

Two types 
One - to -one mergeing:
combine observations from two data sets into a single 
observation in a new data set: 

Match- Merging:combine observations from two data sets into 
a single observation in a new data set according to the 
values of a variable that is specified in the BY statement

total 3 types of mergings are available
they are  one to one merging, one to many merging, many to
many merging

There r four types of merges r there...
match Merge , one to many merge , many to one merge and 
many to many merge

There is 3 types of merge,
1.Equiv Join : Merge the datasets with Only matching   
observations.
2.Non Equiv Join : Merge the datasets with not,greater and 
less matching observations.
3.Outer Join : Merge the datasets with insufficient 
observations.

This the Answer u search for - Types of MERGE

1.One to One reading.
2.Concatenating.
3.Interleaving.
4.Mach Merge.

I'll give the Explanation also, If u need.

7 types 
concatenation
interleving
one to one merge
one to many merge
many to one merge
many to many merge

4 types of merges are present.
they are
1.one to one merging
2.one to many
3.many to one
4.many to many

the types of merge are
1)  one to one merging
2)  match merging

arai uselessfelow why are you dropping these type of 
answers.how can a person knows how many types of merges are 
there?
please don't drop the wrong answers.

Till now, i had used 2 types of Merges...

1 More than 2 datasets having same BY variable...
eg : Adding summary statistics to the Dataset.
2 More than 2 datasets doesnt having same BY variables...
eg : adding totals to the dataset.

hey ashok kore if u know the right answer then post 
otherwise keep quiet(noru musuko) uselessfellow