[Enhancement] documents rebuild with Vuepress (#3408) (#3414)

docs/en/sql-reference/sql-functions/string-functions/get_json_string.md

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+---
+{
+    "title": "get_json_string",
+    "language": "en"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+# get_json_string
+## description
+### Syntax
+
+'VARCHAR get_json_string (VARCHAR json str, VARCHAR json path)
+
+
+Parse and retrieve the string content of the specified path in the JSON string.
+Where json_path must start with the $symbol and use. as the path splitter. If the path contains..., double quotation marks can be used to surround it.
+Use [] to denote array subscripts, starting at 0.
+The content of path cannot contain ",[and].
+If the json_string format is incorrect, or the json_path format is incorrect, or matches cannot be found, NULL is returned.
+
+## example
+
+1. Get the value of key as "k1"
+
+```
+mysql> SELECT get_json_string('{"k1":"v1", "k2":"v2"}', "$.k1");
++---------------------------------------------------+
+| get_json_string('{"k1":"v1", "k2":"v2"}', '$.k1') |
++---------------------------------------------------+
+| v1                                                |
++---------------------------------------------------+
+```
+
+2. Get the second element of the array whose key is "my. key"
+
+```
+mysql> SELECT get_json_string('{"k1":"v1", "my.key":["e1", "e2", "e3"]}', '$."my.key"[1]');
++------------------------------------------------------------------------------+
+| get_json_string('{"k1":"v1", "my.key":["e1", "e2", "e3"]}', '$."my.key"[1]') |
++------------------------------------------------------------------------------+
+| e2                                                                           |
++------------------------------------------------------------------------------+
+```
+
+3. Get the first element in an array whose secondary path is k1. key - > K2
+```
+mysql> SELECT get_json_string('{"k1.key":{"k2":["v1", "v2"]}}', '$."k1.key".k2[0]');
++-----------------------------------------------------------------------+
+| get_json_string('{"k1.key":{"k2":["v1", "v2"]}}', '$."k1.key".k2[0]') |
++-----------------------------------------------------------------------+
+| v1                                                                    |
++-----------------------------------------------------------------------+
+```
+
+4. Get all the values in the array where the key is "k1"
+```
+mysql> SELECT get_json_string('[{"k1":"v1"}, {"k2":"v2"}, {"k1":"v3"}, {"k1":"v4"}]', '$.k1');
++---------------------------------------------------------------------------------+
+| get_json_string('[{"k1":"v1"}, {"k2":"v2"}, {"k1":"v3"}, {"k1":"v4"}]', '$.k1') |
++---------------------------------------------------------------------------------+
+| ["v1","v3","v4"]                                                                |
++---------------------------------------------------------------------------------+
+```
+##keyword
+GET_JSON_STRING,GET,JSON,STRING