json_extract

description

Syntax

`VARCHAR json_extract(VARCHAR json_str, VARCHAR path[, VARCHAR path] ...))`
JSON jsonb_extract(JSON j, VARCHAR json_path)
BOOLEAN json_extract_isnull(JSON j, VARCHAR json_path)
BOOLEAN json_extract_bool(JSON j, VARCHAR json_path)
INT json_extract_int(JSON j, VARCHAR json_path)
BIGINT json_extract_bigint(JSON j, VARCHAR json_path)
LARGEINT json_extract_largeint(JSON j, VARCHAR json_path)
DOUBLE json_extract_double(JSON j, VARCHAR json_path)
STRING json_extract_string(JSON j, VARCHAR json_path)

json_extract functions extract field specified by json_path from JSON. A series of functions are provided for different datatype.

• json_extract with VARCHAR argument, extract and return VARCHAR datatype
• jsonb_extract extract and return JSON datatype
• json_extract_isnull check if the field is json null and return BOOLEAN datatype
• json_extract_bool extract and return BOOLEAN datatype
• json_extract_int extract and return INT datatype
• json_extract_bigint extract and return BIGINT datatype
• json_extract_largeint extract and return LARGEINT datatype
• json_extract_double extract and return DOUBLE datatype
• json_extract_STRING extract and return STRING datatype

json path syntax:

• ‘$’ for json document root
• ‘.k1’ for element of json object with key ‘k1’
  • If the key column value contains “.”, double quotes are required in json_path, For example: SELECT json_extract(‘{“k1.a”:”abc”,”k2”:300}’, ‘$.”k1.a”‘);
• ‘[i]‘ for element of json array at index i
  • Use ‘$[last]‘ to get the last element of json_array, and ‘$[last-1]‘ to get the penultimate element, and so on.

Exception handling is as follows:

• if the field specified by json_path does not exist, return NULL
• if datatype of the field specified by json_path is not the same with type of json_extract_t, return t if it can be cast to t else NULL

json_exists_path and json_type

description

Syntax

BOOLEAN json_exists_path(JSON j, VARCHAR json_path)
STRING json_type(JSON j, VARCHAR json_path)

There are two extra functions to check field existence and type

• json_exists_path check the existence of the field specified by json_path, return TRUE or FALS
• json_type get the type as follows of the field specified by json_path, return NULL if it does not exist
  • object
  • array
  • null
  • bool
  • int
  • bigint
  • largeint
  • double
  • string

example

refer to json tutorial for more.

mysql> SELECT json_extract('{"id": 123, "name": "doris"}', '$.id');
+------------------------------------------------------+
| json_extract('{"id": 123, "name": "doris"}', '$.id') |
+------------------------------------------------------+
| 123                                                  |
+------------------------------------------------------+
1 row in set (0.01 sec)
mysql> SELECT json_extract('[1, 2, 3]', '$.[1]');
+------------------------------------+
| json_extract('[1, 2, 3]', '$.[1]') |
+------------------------------------+
| 2                                  |
+------------------------------------+
1 row in set (0.01 sec)
mysql> SELECT json_extract('{"k1": "v1", "k2": { "k21": 6.6, "k22": [1, 2] } }', '$.k1', '$.k2.k21', '$.k2.k22', '$.k2.k22[1]');
+-------------------------------------------------------------------------------------------------------------------+
| json_extract('{"k1": "v1", "k2": { "k21": 6.6, "k22": [1, 2] } }', '$.k1', '$.k2.k21', '$.k2.k22', '$.k2.k22[1]') |
+-------------------------------------------------------------------------------------------------------------------+
| ["v1",6.6,[1,2],2]                                                                                                |
+-------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
mysql> SELECT json_extract('{"id": 123, "name": "doris"}', '$.aaa', '$.name');
+-----------------------------------------------------------------+
| json_extract('{"id": 123, "name": "doris"}', '$.aaa', '$.name') |
+-----------------------------------------------------------------+
| [null,"doris"]                                                  |
+-----------------------------------------------------------------+
1 row in set (0.01 sec)

keywords

JSONB, JSON, json_extract, json_extract_isnull, json_extract_bool, json_extract_int, json_extract_bigint, json_extract_largeint,json_extract_double, json_extract_string, json_exists_path, json_type