Add extract data from json recipe

other-builtin-functions/07_extract_data_from_json/07_extract_data_from_json.md

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+# 07 Extract data from JSON
+
+![Twitter Badge](https://img.shields.io/badge/Flink%20Version-1.15%2B-lightgrey)
+
+> :bulb: This example will show how you can extract data from JSON using JSON functions.
+
+The source table (`clients`) is backed by the [`faker` connector](https://flink-packages.org/packages/flink-faker), which continuously generates JSON strings in memory based on datafaker expressions.
+
+There are many JSON functions in FlinkSQL. Within this receipt we are going to touch some of them: `IS JSON`, `JSON_EXISTS`, `JSON_VALUE`, `JSON_QUERY`. You can find more information about these and other JSON functions in the [Flink SQL JSON Functions](https://nightlies.apache.org/flink/flink-docs-master/docs/dev/table/functions/systemfunctions/#json-functions).
+
+In this recipe, we'll check whether data in string is a `JSON`, extract some scalar and more complex values from `JSON`.
+
+This table DDL creates a `clients` table. It contains a json with identifier, a full name of a client and an array of addresses (2 elements) to which a company could send mail.
+
+## Script
+
+```sql
+ CREATE TEMPORARY TABLE clients (
+ `json_string` STRING
+ )
+ WITH (
+ 'connector' = 'faker',
+ 'fields.json.expression' = '#{jsona ''-1'',''id'',''#{Internet.uuid}'',''-1'', ''full_name'',''#{Name.full_name}'',''2'',''addresses'',''#{json ''''address'''',''''#{Address.fullAddress}''''}''}'
+ );
+```
+
+After creating the table we are going to use json functions. First let's consider `IS JSON` which could tell if a string is a json or not. The next one is `JSON_EXISTS` which determines whether a json satisfies search path criteria. Here, the special character `$` denotes the root node in a JSON path.
+`JSON_VALUE`: Extracts a scalar from a JSON string. `JSON_QUERY`: Extracts JSON values from a JSON string.
+
+```sql
+ SELECT 
+ json_string IS JSON as `Is JSON`, 
+ JSON_EXISTS(json_string, '$.id') as `Is id present`,
+ JSON_VALUE(json_string, '$.full_name') as `Full Name`,
+ JSON_QUERY(json_string, '$.addresses[*].address') as `Address`,
+ json_string as `Original JSON`
+ FROM clients;
+```
+
+## Example Output
+
+![07_extract_data_from_json](07_extract_data_from_json.gif)