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Updated on 2022-11-09 GMT+08:00
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How Does Flink Opensource SQL Parse Nested JSON?

  • Kafka message
    {
  "id": 1234567890,
  "name": "swq",
  "date": "1997-04-25",
  "obj": {
    "time1": "12:12:12",
    "str": "test",
    "lg": 1122334455
  },
  "arr": [
    "ly",
    "zpk",
    "swq",
    "zjy"
  ],
  "rowinarr": [
    {
      "f1": "f11",
      "f2": 111
    },
    {
      "f1": "f12",
      "f2": 222
    }
  ],
  "time": "13:13:13",
  "timestamp": "1997-04-25 14:14:14",
  "map": {
    "flink": 123
  },
  "mapinmap": {
    "inner_map": {
      "key": 234
    }
  }
}
  • Flink Opensource SQL
    create table kafkaSource(
  id            BIGINT,
  name          STRING,
  `date`        DATE,
  obj           ROW<time1 TIME,str STRING,lg BIGINT>,
  arr           ARRAY<STRING>,
  rowinarr      ARRAY<ROW<f1 STRING,f2 INT>>,
  `time`        TIME,
  `timestamp`   TIMESTAMP(3),
  `map`         MAP<STRING,BIGINT>,
  mapinmap      MAP<STRING,MAP<STRING,INT>>
) with (
  'connector' = 'kafka',
  'topic' = 'topic-swq-3',
  'properties.bootstrap.servers' = '10.128.0.138:9092,10.128.0.119:9092,10.128.0.212:9092',
  'properties.group.id' = 'swq-test',
  'scan.startup.mode' = 'latest-offset',
  'format' = 'json'
);
create table printSink (
  id            BIGINT,
  name          STRING,
  `date`        DATE,
  str           STRING,
  arr           ARRAY<STRING>,
  nameinarray   STRING,
  rowinarr      ARRAY<ROW<f1 STRING,f2 INT>>,
  f2            INT,
  `time`        TIME,
  `timestamp`   TIMESTAMP(3),
  `map`         MAP<STRING,BIGINT>,
  flink         BIGINT,
  mapinmap      MAP<STRING,MAP<STRING,INT>>,
  `key`         INT
) with ('connector' = 'print');
 
insert into
  printSink
select
  id,
  name,
  `date`,
  obj.str,
  arr,
  arr[4],
  rowinarr,
  rowinarr[1].f2,
  `time`,
  `timestamp`,
  `map`,
  `map`['flink'],
  mapinmap,
  mapinmap['inner_map']['key']
from kafkaSource;
  • Result
    +I(1234567890,swq,1997-04-25,test,[ly, zpk, swq, zjy],zjy,[f11,111, f12,222],111,13:13:13,1997-04-25T14:14:14,{flink=123},123,{inner_map={key=234}},234)
  1. Use the following methods to obtain elements in the containers of different types.

    - map: map['key']

    - array: array[index]

    - row: row.key

  2. The index of an array starts from 1. Array[1] is the first element.
  3. The elements of an array must be of the same type, and the elements of a row can be of different types.
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