JSON MySQL 5.7 query
If I've understood you correctly, you want something like this

SELECT * FROM products WHERE JSON_EXTRACT(feature_products, "$.frequency") = '3.99GHz';


I created a table "products" - note that the last record corresponds to the one we want.

SELECT * FROM products;

id_products name_products   feature_products
1   blah    {"cache": {"l1": "128k", "l2": "6Mb"}, "socket": "am3+", "frequency": "3.97GHz"}
1   blah2   {"cache": {"l1": "128k", "l2": "6Mb"}, "socket": "am3+", "frequency": "4.7GHz"}
1   result  {"cache": {"l1": "128k", "l2": "6Mb"}, "socket": "am3+", "frequency": "3.99GHz}


Running the query above 

SELECT * FROM products WHERE JSON_EXTRACT(feature_products, "$.frequency") = '3.99GHz';


gives:

id_products name_products   feature_products
1       result      {"cache": {"l1": "128k", "l2": "6Mb"}, "socket": "am3+", "frequency": "3.99GHz"}"


Which, as we can see, is what was required -  result "frequency" and "3.9GHz" and query for everything

I found this reference helpful. And, if all else fails, one can always consult the documentation here :-). Also, the MySQL server team blog was useful.