>>I think you'll have to script the database and data in SQL2012 and then run those scripts on SQL2008 dealing with any incompatibilities. (if any)
>
>Yes, I have script procedure. But, that database is too big. That is why I had to dump the table into a temporary database, zip, download, upload, unzip, attach.

Do it in smaller chunks. Have scripts for each table which would insert perhaps one megabyte at a time. Use the ability of 2012 to insert multiple records at a time (something MySql had eight years ago) so you don't have to repeat the field names, as 2008 will accept that. Just tried this and it worked in 2008:

insert into tableX (
   cField, intField) VALUES ('blabla',0), ('blabla2', 2)

SQL is simply NOT forwards compatible, it won't even restore a backup from a later version, and I don't know of an utility which would allow you to export a database in a compatible format, other than building a script. Which is exactly the reason I have both 2008 and 2012 running on my box, and I did have to write a generator of insert scripts (doesn't utilize this multiple record insert, as I'm doing it for almost blank databases so I don't need it).