JSON Functions and Operators

PostgreSQL 9.4.4 Documentation
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# 9.15. JSON Functions and Operators

Table 9-40 shows the operators that are available for use with the two JSON data types (see Section 8.14).

Table 9-40. `json` and `jsonb` Operators

Operator | Right Operand Type | Description | Example | Example Result
--- | --- | --- | --- | ---
`->` | `int` | Get JSON array element (indexed from zero) | `'[{"a":"foo"},{"b":"bar"},{"c":"baz"}]'::json->2` | `{"c":"baz"}`
`->` | `text` | Get JSON object field by key | `'{"a": {"b":"foo"}}'::json->'a'` | `{"b":"foo"}`
`->>` | `int` | Get JSON array element as `text` | `'[1,2,3]'::json->>2` | `3`
`->>` | `text` | Get JSON object field as `text` | `'{"a":1,"b":2}'::json->>'b'` | `2`
`#>` | `text[]` | Get JSON object at specified path | `'{"a": {"b":{"c": "foo"}}}'::json#>'{a,b}'` | `{"c": "foo"}`
`#>>` | `text[]` | Get JSON object at specified path as `text` | `'{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}'` | `3`

> Note: There are parallel variants of these operators for both the `json` and `jsonb` types. The field/element/path extraction operators return the same type as their left-hand input (either `json` or `jsonb`), except for those specified as returning `text`, which coerce the value to text. The field/element/path extraction operators return NULL, rather than failing, if the JSON input does not have the right structure to match the request; for example if no such element exists.

The standard comparison operators shown in Table 9-1 are available for `jsonb`, but not for `json`. They follow the ordering rules for B-tree operations outlined at Section 8.14.4.

Some further operators also exist only for `jsonb`, as shown in Table 9-41. Many of these operators can be indexed by `jsonb` operator classes. For a full description of `jsonb` containment and existence semantics, see Section 8.14.3. Section 8.14.4 describes how these operators can be used to effectively index `jsonb` data.

Table 9-41. Additional `jsonb` Operators

Operator | Right Operand Type | Description | Example
--- | --- | --- | ---
`@>` | `jsonb` | Does the left JSON value contain within it the right value? | `'{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb`
`<@` | `jsonb` | Is the left JSON value contained within the right value? | `'{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb`
`?` | `text` | Does the key/element string exist within the JSON value? | `'{"a":1, "b":2}'::jsonb ? 'b'`
`?|` | `text[]` | Do any of these key/element strings exist? | `'{"a":1, "b":2, "c":3}'::jsonb ?| array['b', 'c']`
`?&` | `text[]` | Do all of these key/element strings exist? | `'["a", "b"]'::jsonb ?& array['a', 'b']`

Table 9-42 shows the functions that are available for creating `json` values. (Currently, there are no equivalent functions for `jsonb`, but you can cast the result of one of these functions to `jsonb`.)

Table 9-42. JSON Creation Functions

Function | Description | Example | Example Result
--- | --- | --- | ---
`to_json(anyelement)` | Returns the value as JSON. Arrays and composites are converted (recursively) to arrays and objects; otherwise, if there is a cast from the type to `json`, the cast function will be used to perform the conversion; otherwise, a JSON scalar value is produced. For any scalar type other than a number, a Boolean, or a null value, the text representation will be used, properly quoted and escaped so that it is a valid JSON string. | `to_json('Fred said "Hi."'::text)` | `"Fred said \"Hi.\""`
`array_to_json(anyarray [, pretty_bool])` | Returns the array as a JSON array. A PostgreSQL multidimensional array becomes a JSON array of arrays. Line feeds will be added between dimension-1 elements if `pretty_bool` is true. | `array_to_json('{{1,5},{99,100}}'::int[])` | `[[1,5],[99,100]]`
`row_to_json(record [, pretty_bool])` | Returns the row as a JSON object. Line feeds will be added between level-1 elements if `pretty_bool` is true. | `row_to_json(row(1,'foo'))` | `{"f1":1,"f2":"foo"}`
`json_build_array(VARIADIC "any")` | Builds a possibly-heterogeneously-typed JSON array out of a variadic argument list. | `json_build_array(1,2,'3',4,5)` | `[1, 2, "3", 4, 5]`
`json_build_object(VARIADIC "any")` | Builds a JSON object out of a variadic argument list. By convention, the argument list consists of alternating keys and values. | `json_build_object('foo',1,'bar',2)` | `{"foo": 1, "bar": 2}`
`json_object(text[])` | Builds a JSON object out of a text array. The array must have either exactly one dimension with an even number of members, in which case they are taken as alternating key/value pairs, or two dimensions such that each inner array has exactly two elements, which are taken as a key/value pair. | `json_object('{a, 1, b, "def", c, 3.5}')` `json_object('{{a, 1},{b, "def"},{c, 3.5}}')` | `{"a": "1", "b": "def", "c": "3.5"}`
`json_object(keys text[], values text[])` | This form of `json_object` takes keys and values pairwise from two separate arrays. In all other respects it is identical to the one-argument form. | `json_object('{a, b}', '{1,2}')` | `{"a": "1", "b": "2"}`

> Note: `array_to_json` and `row_to_json` have the same behavior as `to_json` except for offering a pretty-printing option. The behavior described for `to_json` likewise applies to each individual value converted by the other JSON creation functions.

> Note: The hstore extension has a cast from `hstore` to `json`, so that `hstore` values converted via the JSON creation functions will be represented as JSON objects, not as primitive string values.

Table 9-43 shows the functions that are available for processing `json` and `jsonb` values.

Table 9-43. JSON Processing Functions

Function | Return Type | Description | Example | Example Result
--- | --- | --- | --- | ---
`json_array_length(json)` `jsonb_array_length(jsonb)` | `int` | Returns the number of elements in the outermost JSON array. | `json_array_length('[1,2,3,{"f1":1,"f2":[5,6]},4]')` | `5`
`json_each(json)` `jsonb_each(jsonb)` | `setof key text, value json` `setof key text, value jsonb` | Expands the outermost JSON object into a set of key/value pairs. | `select * from json_each('{"a":"foo", "b":"bar"}')` |
     key | value
    -----+-------
     a   | "foo"
     b   | "bar"
`json_each_text(json)` `jsonb_each_text(jsonb)` | `setof key text, value text` | Expands the outermost JSON object into a set of key/value pairs. The returned values will be of type `text`. | `select * from json_each_text('{"a":"foo", "b":"bar"}')` |
     key | value
    -----+-------
     a   | foo
     b   | bar
`json_extract_path(from_json json, VARIADIC path_elems text[])` `jsonb_extract_path(from_json jsonb, VARIADIC path_elems text[])` | `json` `jsonb` | Returns JSON value pointed to by `path_elems` (equivalent to `#>` operator). | `json_extract_path('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4')` | `{"f5":99,"f6":"foo"}`
`json_extract_path_text(from_json json, VARIADIC path_elems text[])` `jsonb_extract_path_text(from_json jsonb, VARIADIC path_elems text[])` | `text` | Returns JSON value pointed to by `path_elems` as `text` (equivalent to `#>>` operator). | `json_extract_path_text('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4', 'f6')` | `foo`
`json_object_keys(json)` `jsonb_object_keys(jsonb)` | `setof text` | Returns set of keys in the outermost JSON object. | `json_object_keys('{"f1":"abc","f2":{"f3":"a", "f4":"b"}}')` |
     json_object_keys
    ------------------
     f1
     f2
`json_populate_record(base anyelement, from_json json)` `jsonb_populate_record(base anyelement, from_json jsonb)` | `anyelement` | Expands the object in `from_json` to a row whose columns match the record type defined by `base` (see note below). | `select * from json_populate_record(null::myrowtype, '{"a":1,"b":2}')` |
     a | b
    ---+---
     1 | 2
`json_populate_recordset(base anyelement, from_json json)` `jsonb_populate_recordset(base anyelement, from_json jsonb)` | `setof anyelement` | Expands the outermost array of objects in `from_json` to a set of rows whose columns match the record type defined by `base` (see note below). | `select * from json_populate_recordset(null::myrowtype, '[{"a":1,"b":2},{"a":3,"b":4}]')` |
     a | b
    ---+---
     1 | 2
     3 | 4
`json_array_elements(json)` `jsonb_array_elements(jsonb)` | `setof json` `setof jsonb` | Expands a JSON array to a set of JSON values. | `select * from json_array_elements('[1,true, [2,false]]')` |
       value
    -----------
     1
     true
     [2,false]
`json_array_elements_text(json)` `jsonb_array_elements_text(jsonb)` | `setof text` | Expands a JSON array to a set of `text` values. | `select * from json_array_elements_text('["foo", "bar"]')` |
       value
    -----------
     foo
     bar
`json_typeof(json)` `jsonb_typeof(jsonb)` | `text` | Returns the type of the outermost JSON value as a text string. Possible types are `object`, `array`, `string`, `number`, `boolean`, and `null`. | `json_typeof('-123.4')` | `number`
`json_to_record(json)` `jsonb_to_record(jsonb)` | `record` | Builds an arbitrary record from a JSON object (see note below). As with all functions returning `record`, the caller must explicitly define the structure of the record with an `AS` clause. | `select * from json_to_record('{"a":1,"b":[1,2,3],"c":"bar"}') as x(a int, b text, d text)` |
     a |    b    | d
    ---+---------+---
     1 | [1,2,3] |
`json_to_recordset(json)` `jsonb_to_recordset(jsonb)` | `setof record` | Builds an arbitrary set of records from a JSON array of objects (see note below). As with all functions returning `record`, the caller must explicitly define the structure of the record with an `AS` clause. | `select * from json_to_recordset('[{"a":1,"b":"foo"},{"a":"2","c":"bar"}]') as x(a int, b text);` |
     a |  b
    ---+-----
     1 | foo
     2 |

> Note: Many of these functions and operators will convert Unicode escapes in JSON strings to the appropriate single character. This is a non-issue if the input is type `jsonb`, because the conversion was already done; but for `json` input, this may result in throwing an error, as noted in Section 8.14.

> Note: In `json_populate_record`, `json_populate_recordset`, `json_to_record` and `json_to_recordset`, type coercion from the JSON is "best effort" and may not result in desired values for some types. JSON keys are matched to identical column names in the target row type. JSON fields that do not appear in the target row type will be omitted from the output, and target columns that do not match any JSON field will simply be NULL.

> Note: The `json_typeof` function's `null` return value should not be confused with a SQL NULL. While calling `json_typeof('null'::json)` will return `null`, calling `json_typeof(NULL::json)` will return a SQL NULL.

See also Section 9.20 for the aggregate function `json_agg` which aggregates record values as JSON, and the aggregate function `json_object_agg` which aggregates pairs of values into a JSON object.

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