Insert into

create table dba.tbl_member (member_name varchar(20))
create table dba.tbl_donor  (donor_name varchar(20))

INSERT INTO dba.tbl_member Values ( 'USA')
INSERT INTO dba.tbl_member Values ( 'CANADA')
INSERT INTO dba.tbl_member Values ( 'MEXICO')

INSERT INTO dba.tbl_donor Values ( 'USA')
INSERT INTO dba.tbl_donor Values ( 'ASIA')
INSERT INTO dba.tbl_donor Values ( 'BRAZIL')

select * from dba.tbl_member
select * from dba.tbl_donor

-- Now I need to insert all donor_name values from dba.tbl_donor to member_name.tbl_member table.
-- BUT IF the same name already exists in dba.tbl_member then prefix it with 'DL-' and insert else insert the name from 2nd to first table.
-- So here USA exists in both tables so insert 'DL-USA' in dba.tbl_member and then the rest 2 rows.

INSERT INTO dba.tbl_member (member_name)
(SELECT CASE WHEN a.donor_name =b.member_name THEN 'DL-' + substring(a.donor_name, 1, LEN(a.donor_name))  
ELSE a.donor_name END AS member_name FROM dba.tbl_donor a,dba.tbl_member b) -- BUT I THINK MY THIS QUERY NEEDS YOUR HELP
FROM dba.tbl_donor

So for this scenario I should be able to see total 6 rows in dba.tbl_member after insert.