Upgrade Bucket of document

Suppose i have one bucket and there are several document.After Some days of development i need to add new data on document.How can i add same data in all documents of a bucket ??

It is JOSN and schema less. If you need add new field to document, you don’t have to add all the documents, you can add only documents you need.

Example:  "k1" -  {"a":1, "b":2}  , "k2"  - {"a":10, "c":20}
If you use N1QL   get the documents that has only field b
                    SELECT * FROM default WHERE b IS NOT MISSING;

If you want update  all documents with x 
UPDATE default SET x = "Hello" WHERE ....