Syntax:
column->>path

This is an improved, unquoting extraction operator available in MySQL
5.7.13 and later. Whereas the -> operator simply extracts a value, the
->> operator in addition unquotes the extracted result. In other words,
given a JSON column value column and a path expression path, the
following three expressions return the same value:

o JSON_UNQUOTE( JSON_EXTRACT(column, path) )

o JSON_UNQUOTE(column -> path)

o column->>path

The ->> operator can be used wherever JSON_UNQUOTE(JSON_EXTRACT())
would be allowed. This includes (but is not limited to) SELECT lists,
WHERE and HAVING clauses, and ORDER BY and GROUP BY clauses.

URL: http://dev.mysql.com/doc/refman/5.7/en/json-search-functions.html

