@Override
  public Pattern<ApplyNode> getPattern() {
    return PATTERN;
  }
This rule updates ApplyNode's correlation list. A symbol can be removed from the correlation list
if it is not referenced by the subquery node. Note: This rule does not restrict ApplyNode's
children outputs. It requires additional information about context (symbols required by the outer
plan) and is done in PruneApplyColumns rule.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/relational/planner/iterative/rule/PruneApplyCorrelation.java