Mysql – Working with JSON data MySQL

I am finding that documentation for working with MySQL JSON data is still at this point apparently at it's infancy. Either that or I'm doing it wrong.
I found several docs online, i.e. https://benjaminlistwon.com/blog/working-with-json-data-in-mysql-part-1-of-3/ and others – but neither are working for me.

I recently switched from storing the station data in separate tables per station (4,100+ tables I had to do a "dynamic" PHP query on to get the data – wow!) – to JSON for speed and performance reasons, and an added benifit of not doing 4200 table writes per hour.

To get the aggregate data it's much faster – for a single row of data I can just iterate through the JSON keys. Problem is that to pull data from 83+ rows where Key=Value, PHP says out of memory error. My guess is that means I need to match the JSON value in the query instead of in PHP.

Below: SQL dump of a JSON based data table, StationData. Weather data from various stations collected hourly.

https://drive.google.com/open?id=0B6ScTEIoK3tPbGhrZkJOZmhRUTQ

Problem I'm having is features like JSON_EXTRACT, JSON_SEARCH, and JSON_etc are just returning NULL.

For example, for Olathe Kansas, I want every data stored under {"KOJC":{"Temperature":"25", "Dewpoint":"23"}} etc etc – but nothing from any other keys. The key is KOJC.
(for giggles tried the MySQL doc example):

select JSON_KEYS('{"a": 1, "b": {"c": 30}}');
+---------------------------------------+
| JSON_KEYS('{"a": 1, "b": {"c": 30}}') |
+---------------------------------------+
| ["a", "b"]                            |
+---------------------------------------+
1 row in set (0.02 sec)

select JSON_KEYS(jsonData) from StationData;
+---------------------+
| JSON_KEYS(jsonData) |
+---------------------+
| NULL                |

etc… 85 rows blah blah

select JSON_EXTRACT(jsonData, "$.KOJC") from StationData;

+----------------------------------+
| JSON_EXTRACT(jsonData, "$.KOJC") |
+----------------------------------+
| NULL                             |
| NULL                             |

etc….
85 rows in set (0.16 sec)

select jsonData->>'$.KOJC' as Station from StationData;
+---------+
| Station |
+---------+
| NULL    |

etc….
85 rows in set (0.14 sec)

select * from StationData were JSON_SEARCH(jsonData, 'all', '$.KOJC');
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'JSON_SEARCH(jsonData, 'all', '$.KOJC')' at line 1

select * from StationData where JSON_EXTRACT(jsonData, "$.KOJC");
Empty set (0.15 sec)

UPDATE – I found what's happening. JSON_EXTRACT works for a non-arrayed JSON string but when working with an array I am unable to pull out array elements.

select JSON_EXTRACT('{"KOJC":{"Tmp":"25"}}', '$.KOJC');                          +-------------------------------------------------+
| JSON_EXTRACT('{"KOJC":{"Tmp":"25"}}', '$.KOJC') |
+-------------------------------------------------+
| {"Tmp": "25"}                                   |
+-------------------------------------------------+
1 row in set (0.01 sec)

^ that works
But the below does not when presented with a array:

select JSON_EXTRACT('[{"KOJC":{"Tmp":"25"}}, {"KTWX":{"Tmp":"32"}}]', '$.KOJC');
 +--------------------------------------------------------------------------+
| JSON_EXTRACT('[{"KOJC":{"Tmp":"25"}}, {"KTWX":{"Tmp":"32"}}]', '$.KOJC') |
+--------------------------------------------------------------------------+
| NULL                                                                     |
+--------------------------------------------------------------------------+
1 row in set (0.00 sec)

select JSON_EXTRACT('[{"KOJC":{"Tmp":"25"}}, {"KTWX":{"Tmp":"32"}}]', '$[KOJC][*]');
ERROR 3143 (42000): Invalid JSON path expression. The error is around character position 2.

select JSON_EXTRACT('[{"KOJC":{"Tmp":"25"}}, {"KTWX":{"Tmp":"32"}}]', '$[$.KOJC][*]');
ERROR 3143 (42000): Invalid JSON path expression. The error is around character position 2.