Answer: Dot (.)

The dot (.) operator is used in Spark SQL to navigate through the nested structure of a JSON object. For example, if you have a JSON string in a column named `json_data` with content like `{"name": "John Doe", "age": 30, "address": {"city": "New York", "country": "USA"}}`, you can access the "city" field within the "address" subfield by using the expression `SELECT json_data.address.city FROM your_table_name;`. This will return "New York". The dot operator allows for chaining to access deeper levels within the JSON.

Author: LeetQuiz Editorial Team