Major Description
This JIRA is for submitting a PR for new EXISTS/NOT EXISTS subquery test cases. It follows the same idea as the IN subquery test cases which contain simple patterns, then build more complex constructs in both parent and subquery sides. This batch of test cases are mostly, if not all, positive test cases that do not return any syntax errors or unsupported functionality. We make effort to have test cases returning rows in the result set so that they can indirectly detect incorrect result problems.
