如何迭代Presto数组(MAP(VARCHAR，VARCHAR))

Question

我有一个映射数组(无序键-值对)，并希望过滤出该数组中在2019-01-01之前没有创建或修改日期的任何映射项。有没有办法在没有嵌套表的情况下用presto实现这一点(我必须迭代多个以这种方式构造的列)？

在此之前

+-----------+-------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+--+--+
| Category1 | Count_Items | Item_Details                                                                                                                                               |  |  |
+===========+=============+============================================================================================================================================================+==+==+
| Fruit     | 3           | [{"created":"2019-09-15","color":"red","name":"apples"},{"name":"bananas","created":"2018-08-20"},{"modified":"2019-02-01","name":"kiwi","color":"green"}] |  |  |
| Vegetable | 2           | [{"color":"green","modified":"2018-01-01","created":"2019-03-31","name":"kale"},{"name":"cauliflower","created":"2019-01-02"}]                             |  |  |
+-----------+-------------+------------------------------------------------------------------------------------------------------------------------------------------------------------+--+--+

之后

+-----------+-------------+----------------------------------------------------------------------------------+--+--+
| Category1 | Count_Items | Item_Details                                                                     |  |  |
+===========+=============+==================================================================================+==+==+
| Fruit     | 1           | [{"name":"bananas","created":"2018-08-20"}]                                      |  |  |
| Vegetable | 1           | [{"color":"green","modified":"2018-01-01","created":"2019-03-31","name":"kale"}] |  |  |
+-----------+-------------+----------------------------------------------------------------------------------+--+--+

Answer 1

您需要使用数组filter --您有array(map)，并且希望有array(map)。为此，您需要为filter (一个λ)构造过滤器函数。

(如果您需要更详细的说明，请告诉我。)