public final boolean isConstantOperand() {
    if (isConstantOperandCache == null) {
      isConstantOperandCache = isConstantOperandInternal();
    }
    return isConstantOperandCache;
  }
If this expression and all of its sub-expressions are {@link ConstantOperand}.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/queryengine/plan/expression/Expression.java