Following are the fields you need to set 0 or 1 in core_config_data table to merge / unmergae css/js files.

dev/js/merge_files  - Merge Js
update core_config_data set value=0 where path='dev/js/merge_files';

dev/css/merge_css_files - Merge css 
update core_config_data set value=0 where path='dev/css/merge_css_files' limit 20;