JSON_EXTRACT_PATH_TEXT function - Amazon Redshift
SyntaxArgumentsReturn typeExamples

JSON_EXTRACT_PATH_TEXT function

Note

JSON_PARSE and its associated functions parse JSON values as SUPER, which Amazon Redshift parses more efficiently than VARCHAR.

Instead of using JSON_EXTRACT_PATH_TEXT, we recommend that you parse your JSON strings using the JSON_PARSE function to get a SUPER value. Then, query the element you want using the value.attribute syntax. For more information on querying array elements in SUPER values, go to Querying semistructured data.

The JSON_EXTRACT_PATH_TEXT function returns the value for the key-value pair referenced by a series of path elements in a JSON string. The JSON path can be nested up to five levels deep. Path elements are case-sensitive. If a path element does not exist in the JSON string, JSON_EXTRACT_PATH_TEXT returns NULL.

If the null_if_invalid argument is set to TRUE and the JSON string is invalid, the function returns NULL instead of returning an error.

JSON_EXTRACT_PATH_TEXT has a 64KB data-size maximum. Thus, if any JSON record is larger than 64KB, processing it with JSON_EXTRACT_PATH_TEXT results in an error.

For information about additional JSON functions, see JSON functions. For more information about working with JSON, see COPY from JSON format.

Syntax

JSON_EXTRACT_PATH_TEXT('json_string', 'path_elem' [,'path_elem'[, …] ] [, null_if_invalid ] )

Arguments

json_string

A properly formatted JSON string.

path_elem

A path element in a JSON string. One path element is required. Additional path elements can be specified, up to five levels deep.

null_if_invalid

(Optional) A BOOLEAN value that specifies whether to return NULL if the input JSON string is invalid instead of returning an error. To return NULL if the JSON is invalid, specify TRUE (t). To return an error if the JSON is invalid, specify FALSE (f). The default is FALSE.

In a JSON string, Amazon Redshift recognizes \n as a newline character and \t as a tab character. To load a backslash, escape it with a backslash (\\). For more information, see Escape characters in JSON.

Return type

VARCHAR

A VARCHAR string representing the JSON value referenced by the path elements.

Examples

To return the value for the path 'f4', 'f6', use the following example.

SELECT JSON_EXTRACT_PATH_TEXT('{"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}}','f4', 'f6');

+------------------------+
| json_extract_path_text |
+------------------------+
| star                   |
+------------------------+

To return an error because the JSON is invalid, use the following example.

SELECT JSON_EXTRACT_PATH_TEXT('{"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}','f4', 'f6');

ERROR: invalid json object {"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}

To set null_if_invalid to TRUE, so the statement returns NULL for invalid JSON instead of returning an error, use the following example.

SELECT JSON_EXTRACT_PATH_TEXT('{"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}','f4', 'f6',true);

+------------------------+
| json_extract_path_text |
+------------------------+
| NULL                   |
+------------------------+

Consider the following example, which selects the value for the path 'farm', 'barn', 'color', where the value retrieved is at the third level, use the following example. This sample is formatted with a JSON lint tool, to make it easier to read.

SELECT JSON_EXTRACT_PATH_TEXT('{
    "farm": {
        "barn": {
            "color": "red",
            "feed stocked": true
        }
    }
}', 'farm', 'barn', 'color');
+------------------------+
| json_extract_path_text |
+------------------------+
| red                    |
+------------------------+

To return NULL because the 'color' element is missing, use the following example. This sample is formatted with a JSON lint tool.

SELECT JSON_EXTRACT_PATH_TEXT('{
    "farm": {
        "barn": {}
    }
}', 'farm', 'barn', 'color');

+------------------------+
| json_extract_path_text |
+------------------------+
| NULL                   |
+------------------------+

If the JSON is valid, trying to extract an element that's missing returns NULL.

To return the value for the path 'house', 'appliances', 'washing machine', 'brand', use the following example.

SELECT JSON_EXTRACT_PATH_TEXT('{
  "house": {
    "address": {
      "street": "123 Any St.",
      "city": "Any Town",
      "state": "FL",
      "zip": "32830"
    },
    "bathroom": {
      "color": "green",
      "shower": true
    },
    "appliances": {
      "washing machine": {
        "brand": "Any Brand",
        "color": "beige"
      },
      "dryer": {
        "brand": "Any Brand",
        "color": "white"
      }
    }
  }
}', 'house', 'appliances', 'washing machine', 'brand');  

+------------------------+
| json_extract_path_text |
+------------------------+
| Any Brand              |
+------------------------+

The following example creates a sample table and populates it with SUPER values, then returns the value for the path 'f2' for both rows.

CREATE TABLE json_example(id INT, json_text SUPER);

INSERT INTO json_example VALUES
(1, JSON_PARSE('{"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}}')),
(2, JSON_PARSE('{
    "farm": {
        "barn": {
            "color": "red",
            "feed stocked": true
        }
    }
}'));

SELECT * FROM json_example;
id          | json_text
------------+--------------------------------------------
1           | {"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}}
2           | {"farm":{"barn":{"color":"red","feed stocked":true}}}
 

SELECT id, JSON_EXTRACT_PATH_TEXT(JSON_SERIALIZE(json_text), 'f2') FROM json_example;
         
id          | json_text
------------+--------------------------------------------
1           | {"f3":1}
2           |

Consider the following example statements. The provided path_elem is NULL, so JSON_EXTRACT_PATH_TEXT returns NULL regardless of the value of any other parameters. 

--Statement where path_elem is NULL and json_string is valid JSON.
SELECT JSON_EXTRACT_PATH_TEXT('{"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}}',NULL);

 json_extract_path_text
------------------------
                   NULL

--Statement where only one path_elem is NULL.
SELECT JSON_EXTRACT_PATH_TEXT('{"f2":{"f3":1},"f4":{"f5":99,"f6":"star"}}','f4',NULL);

 json_extract_path_text
------------------------
                   NULL
                   
--Statement where path_elem is NULL and json_string is invalid JSON.
SELECT json_extract_path_text('invalid_json', NULL);

 json_extract_path_text
------------------------
                   NULL

--Statement where path_elem is NULL and null_if_invalid is FALSE.
SELECT json_extract_path_text(NULL, 0, FALSE);

 json_extract_path_text
------------------------
                   NULL

Consider the following example statements. When null_if_invalid is TRUE, JSON_EXTRACT_PATH_TEXT returns NULL when json_string is invalid JSON. If null_if_invalid is FALSE or isn’t set, the function returns an error when json_string is invalid.

--Statement with invalid JSON where null_if_invalid is TRUE.
SELECT json_extract_path_text('invalid_json', 0, TRUE);

 json_extract_path_text
------------------------
                   NULL
                                                    
--Statement with invalid JSON where null_if_invalid is FALSE.
SELECT json_extract_path_text('invalid_json', 0, FALSE);

ERROR:  JSON parsing error

Consider the following examples, where json_string is valid JSON, and path_elem refers to a JSON null value. In this case, JSON_EXTRACT_PATH_TEXT returns NULL. Similarly, when path_elem refers to a non-existing value, JSON_EXTRACT_PATH_TEXT returns NULL, regardless of the value of null_if_invalid.

--Statement selecting a null value.
SELECT json_extract_path_text('[null]', 0);

  json_extract_path_text  
-------------------------
                    NULL   
                             
--Statement selecting a non-existing value.               
SELECT json_extract_path_text('{}', 'a');
       
  json_extract_path_text  
-------------------------
                    NULL