| PostgreSQL 9.4.1 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_jsonandrow_to_jsonhave the same behavior asto_jsonexcept for offering a pretty-printing option. The behavior described forto_jsonlikewise 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_recordandjson_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.