from_json
from_json介绍
from_json(jsonStr, schema[, options]) - 根据给定的 jsonStr 和 schema 返回一个结构体（struct）值。
Examples:
> SELECT from_json('{"a":1, "b":0.8}', 'a INT, b DOUBLE');
{"a":1,"b":0.8}
> SELECT from_json('{"time":"26/08/2015"}', 'time Timestamp', map('timestampFormat', 'dd/MM/yyyy'));
{"time":2015-08-26 00:00:00}
> SELECT from_json('{"teacher": "Alice", "student": [{"name": "Bob", "rank": 1}, {"name": "Charlie", "rank": 2}]}', 'STRUCT<teacher: STRING, student: ARRAY<STRUCT<name: STRING, rank: INT>>>');
{"teacher":"Alice","student":[{"name":"Bob","rank":1},{"name":"Charlie","rank":2}]}Since: 2.2.0