Answer: EXIST

In Spark SQL, Higher Order Functions are designed to work with complex data types by applying functions to each element. The functions include: - **FILTER**: Selects elements based on a specified condition. - **TRANSFORM**: Modifies each element according to a given function. - **MAP**: Applies a function to every element in an array or map. - **REDUCE**: Combines elements into a single value using a function. The **EXIST** function, however, does not fall under the category of Higher Order Functions in Spark SQL. Therefore, **EXIST** is the correct answer as it is not a Higher Order Function.

Author: LeetQuiz Editorial Team