Updating specific column from other table in Oracle

Hi I need to update deal_end_date in main table with matching deal_id and group_id and if deal_end_date does not match to the update table. i need a correlated update script that will work in oracle 11g

main table (before update)

DEAL_ID DEAL_END_DT GROUP_ID
1-----------1/1/2015----------- 12
1----------- 1/1/2015----------- 13
2 ----------- 1/2/2015----------- 12
3 -----------1/3/2015----------- 13

update table

DEAL_ID DEAL_END_DT GROUP_ID
1 ----------- 1/4/2015----------- 12
3 ----------- 1/1/2015----------- 13
4----------- 1/2/2015----------- 13

main table (after update)

DEAL_ID DEAL_END_DT GROUP_ID
1----------- 1/4/2015 -----------12
1----------- 1/1/2015 -----------13
2----------- 1/2/2015 -----------12
3----------- 1/1/2015 -----------13
4----------- 1/2/2015 -----------13

cheers

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