Home |  MySQL Buzz |  FAQ |  Feeds |  Submit your blog feed |  Feedback |  Archive |  Aggregate feed RSS 2.0 English Deutsch Español Français Italiano 日本語 Русский Português 中文
MySQL and PostgreSQL JSON functions: do they differ much?
+2 Vote Up -0 Vote Down
As author of MySQL JSON functions I am also interested in how development goes in another parties. JSON functions and operators in PostgreSQL, indeed, have great features. Some of them, such as operators, I can not do using UDF functions only. But lets see how these functions are interchangeable.

Note: all PostgreSQL examples were taken from PostgreSQL documentation.

First topic is syntax sugar.

 PostgreSQL MySQL

Operator ->

postgres=# select '[1,2,3]'::json->2;
 ?column?
----------
 3
(1 row)

postgres=# select '{"a":1,"b":2}'::json->'b';
 ?column?
----------
 2
(1 row)


JSON_EXTRACT

mysql> select json_extract('[1,2,3]', 2);
+----------------------------+
| json_extract('[1,2,3]', 2) |
+----------------------------+
| 3                          |
+----------------------------+
1 row in set (0.00 sec)

mysql> select json_extract('{"a":1,"b":2}', 'b');
+------------------------------------+
| json_extract('{"a":1,"b":2}', 'b') |
+------------------------------------+
| 2                                  |
+------------------------------------+
1 row in set (0.00 sec)

Operator ->>

postgres=# select '[1,2,3]'::json->>2;
 ?column?
----------
 3
(1 row)

postgres=# select '{"a":1,"b":2}'::json->>'b';
 ?column?
----------
 2
(1 row)


JSON_EXTRACT

mysql> select json_extract('[1,2,3]', 2);
+----------------------------+
| json_extract('[1,2,3]', 2) |
+----------------------------+
| 3                          |
+----------------------------+
1 row in set (0.00 sec)

mysql> select json_extract('{"a":1,"b":2}', 'b');
+------------------------------------+
| json_extract('{"a":1,"b":2}', 'b') |
+------------------------------------+
| 2                                  |
+------------------------------------+
1 row in set (0.00 sec)

Operator #>

postgres=# select '{"a":[1,2,3],"b":[4,5,6]}'::json#>'{a,2}';
 ?column?
----------
 3
(1 row)


JSON_EXTRACT

mysql> select json_extract('{"a":[1,2,3],"b":[4,5,6]}', 'a', 2);
+---------------------------------------------------+
| json_extract('{"a":[1,2,3],"b":[4,5,6]}', 'a', 2) |
+---------------------------------------------------+
| 3                                                 |
+---------------------------------------------------+
1 row in set (0.00 sec)

Operator #>>

postgres=# select '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}';
 ?column?
----------
 3
(1 row)

JSON_EXTRACT

mysql> select json_extract('{"a":[1,2,3],"b":[4,5,6]}', 'a', 2);
+---------------------------------------------------+
| json_extract('{"a":[1,2,3],"b":[4,5,6]}', 'a', 2) |
+---------------------------------------------------+
| 3                                                 |
+---------------------------------------------------+
1 row in set (0.00 sec)


Then PostgreSQL JSON functions

 PostgreSQL  MySQL array_to_json(anyarray [, pretty_bool])  Not supported row_to_json(record [, pretty_bool])  Not supported to_json(anyelement)  Not supported json_array_length(json)  Not supported, planned as bug #70580 json_each(json)  Not supported, cannot be implemented using UDFs only
json_each_text(from_json json)  Not supported, cannot be implemented using UDFs only

json_extract_path(from_json json, VARIADIC path_elems text[])


postgres=# select json_extract_path('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4');
  json_extract_path   
----------------------
 {"f5":99,"f6":"foo"}
(1 row)

JSON_EXTRACT

mysql> select json_extract('{"f2":{"f3":1},\c

"f4":{"f5":99,"f6":"foo"}}','f4');
+---------------------------------+
| json_extract('{"f2":{"f3":1},

"f4":{"f5":99,"f6":"foo"}}','f4') |
+---------------------------------+
| {"f5":99,"f6":"foo"}            |
+---------------------------------+
1 row in set (0.00 sec)

json_extract_path_text(from_json json, VARIADIC path_elems text[])


postgres=# select json_extract_path_text('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4', 'f6');
 json_extract_path_text
------------------------
 foo
(1 row)

 JSON_EXTRACT

select json_extract('{"f2":{"f3":1},\c

"f4":{"f5":99,"f6":"foo"}}','f4', 'f6');
+---------------------------------------+
| json_extract('{"f2":{"f3":1},

"f4":{"f5":99,"f6":"foo"}}','f4', 'f6') |
+---------------------------------------+
| foo                                   |
+---------------------------------------+
1 row in set (0.01 sec)

json_object_keys(json)  Not supported, cannot be implemented using UDFs only json_populate_record(base anyelement, from_json json, [, use_json_as_text bool=false]  Not supported, cannot be implemented using UDFs only json_populate_recordset(base anyelement, from_json json, [, use_json_as_text bool=false]  Not supported, cannot be implemented using UDFs only json_array_elements(json)  Not supported, cannot be implemented using UDFs only

And, finally, MySQL functions

 MySQL  PostgreSQL json_append  Not supported, but user can convert JSON value into various formats, then create new JSON document from it json_contains_key  Not supported, however has function json_object_keys(json)
json_extract  Supported in numerous ways, see above json_merge   Not supported, but user can convert JSON value into various formats, then create new JSON document from it json_remove   Not supported, but user can convert JSON value into various formats, then create new JSON document from it  json_replace
  Not supported, but user can convert JSON value into various formats, then create new JSON document from it json_search  Not supported
json_set   Not supported, but user can convert JSON value into various formats, then create new JSON document from it json_test_parser   Not supported json_valid  Not supported, however it has JSON type and checks every element for validity

As a conclusion I can say that MySQL and PostgreSQL implementations mostly intersect in extracting elements while solve element validation and manipulation tasks in different ways.

Votes:

You must be logged in with a MySQL account to vote on Planet MySQL entries. More information on PlanetMySQL voting.

Planet MySQL © 1995, 2014, Oracle Corporation and/or its affiliates   Legal Policies | Your Privacy Rights | Terms of Use

Content reproduced on this site is the property of the respective copyright holders. It is not reviewed in advance by Oracle and does not necessarily represent the opinion of Oracle or any other party.