关于json和jsonb数据类型之间的差异，值得一提的是官方的解释:

PostgreSQL offers two types for storing JSON data: json and jsonb. To implement efficient query mechanisms for these data types, PostgreSQL also provides the jsonpath data type described in Section 8.14.6. The json and jsonb data types accept almost identical sets of values as input. The major practical difference is one of efficiency. The json data type stores an exact copy of the input text, which processing functions must reparse on each execution; while jsonb data is stored in a decomposed binary format that makes it slightly slower to input due to added conversion overhead, but significantly faster to process, since no reparsing is needed. jsonb also supports indexing, which can be a significant advantage. Because the json type stores an exact copy of the input text, it will preserve semantically-insignificant white space between tokens, as well as the order of keys within JSON objects. Also, if a JSON object within the value contains the same key more than once, all the key/value pairs are kept. (The processing functions consider the last value as the operative one.) By contrast, jsonb does not preserve white space, does not preserve the order of object keys, and does not keep duplicate object keys. If duplicate keys are specified in the input, only the last value is kept. In general, most applications should prefer to store JSON data as jsonb, unless there are quite specialized needs, such as legacy assumptions about ordering of object keys. PostgreSQL allows only one character set encoding per database. It is therefore not possible for the JSON types to conform rigidly to the JSON specification unless the database encoding is UTF8. Attempts to directly include characters that cannot be represented in the database encoding will fail; conversely, characters that can be represented in the database encoding but not in UTF8 will be allowed.

来源:https://www.postgresql.org/docs/current/datatype-json.html

Peeyush:

简单的回答是:

如果你在PostgreSQL中做很多JSON操作，比如排序、切片、拼接等，出于速度考虑，你应该使用JSONB。 如果需要对JSON上的任意键搜索进行索引查找，那么应该使用JSONB。 如果以上两种方法都不使用，则可能应该使用JSON。 如果需要保留键顺序、空格和重复的键，则应该使用JSON。

想要得到更长的答案，你需要等我在9.4发行版之前写一篇完整的“HowTo”文章。

据我所知

hstore as it currently exists (in PostgreSQL 9.3) does not allow for nesting other objects and arrays as the values of its key/value pairs. However, a future hstore patch will allow for nesting. This patch will not be in the 9.4 release and may not be included any time soon. json as it currently exists does allow for nesting, but it is text-based and does not allow for indexing, thus it is "slow" jsonb that will be released with 9.4 will have the current nesting capabilities of json, as well as the GIN/GIST indexing of hstore, so it will be fast

开发PostgreSQL 9.4的人似乎在说，新的、快速的jsonb类型将吸引那些选择使用像MongoDB这样的NoSQL数据存储的人，但它现在可以将关系数据库和可查询的非结构化数据组合在一个框架下

为什么HStore2/jsonb是9.4最重要的补丁

PostgreSQL 9.4 jsonb的基准测试似乎与MongoDB相当，在某些情况下甚至比MongoDB更快。

http://texture.io/alphabetum/postgresql-incl-hstore-vs-mongodb

hstore is more of a "wide column" storage type, it is a flat (non-nested) dictionary of key-value pairs, always stored in a reasonably efficient binary format (a hash table, hence the name). json stores JSON documents as text, performing validation when the documents are stored, and parsing them on output if needed (i.e. accessing individual fields); it should support the entire JSON spec. Since the entire JSON text is stored, its formatting is preserved. jsonb takes shortcuts for performance reasons: JSON data is parsed on input and stored in binary format, key orderings in dictionaries are not maintained, and neither are duplicate keys. Accessing individual elements in the JSONB field is fast as it doesn't require parsing the JSON text all the time. On output, JSON data is reconstructed and initial formatting is lost.

在我看来，如果您处理的是机器可读的数据，那么一旦jsonb可用，就没有什么重要的理由不使用它。

关于json和jsonb数据类型之间的差异，值得一提的是官方的解释:

PostgreSQL offers two types for storing JSON data: json and jsonb. To implement efficient query mechanisms for these data types, PostgreSQL also provides the jsonpath data type described in Section 8.14.6. The json and jsonb data types accept almost identical sets of values as input. The major practical difference is one of efficiency. The json data type stores an exact copy of the input text, which processing functions must reparse on each execution; while jsonb data is stored in a decomposed binary format that makes it slightly slower to input due to added conversion overhead, but significantly faster to process, since no reparsing is needed. jsonb also supports indexing, which can be a significant advantage. Because the json type stores an exact copy of the input text, it will preserve semantically-insignificant white space between tokens, as well as the order of keys within JSON objects. Also, if a JSON object within the value contains the same key more than once, all the key/value pairs are kept. (The processing functions consider the last value as the operative one.) By contrast, jsonb does not preserve white space, does not preserve the order of object keys, and does not keep duplicate object keys. If duplicate keys are specified in the input, only the last value is kept. In general, most applications should prefer to store JSON data as jsonb, unless there are quite specialized needs, such as legacy assumptions about ordering of object keys. PostgreSQL allows only one character set encoding per database. It is therefore not possible for the JSON types to conform rigidly to the JSON specification unless the database encoding is UTF8. Attempts to directly include characters that cannot be represented in the database encoding will fail; conversely, characters that can be represented in the database encoding but not in UTF8 will be allowed.

来源:https://www.postgresql.org/docs/current/datatype-json.html

JSONB是JSON的“更好”版本。

让我们来看一个例子:

SELECT '{"c":0,   "a":2,"a":1}'::json, '{"c":0,   "a":2,"a":1}'::jsonb;

          json          |        jsonb 
------------------------+--------------------- 
 {"c":0,   "a":2,"a":1} | {"a": 1, "c": 0} 
(1 row)

JSON stores white space, and that is why we can see spaces when key "a" is stored, while JSONB does not. JSON stores all the values of a key. This is the reason you can see multiple values (2 and 1) against the key "a" , while JSONB only "stores" the last value. JSON maintains the order in which elements are inserted, while JSONB maintains the "sorted" order. JSONB objects are stored as a decompressed binary as opposed to "raw data" in JSON, where no reparsing of data is required during retrieval. JSONB also supports indexing, which can be a significant advantage.

一般来说，应该更喜欢JSONB，除非有特殊的需要，比如对对象键的顺序有遗留的假设。