PostgreSQL 9.3beta1 Documentation | ||||
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Table 9-39 shows the operators that are available for use with JSON (see Section 8.14) data.
Table 9-39. JSON Operators
Operator | Right Operand Type | Description | Example |
---|---|---|---|
-> | int | Get JSON array element | '[1,2,3]'::json->2 |
-> | text | Get JSON object field | '{"a":1,"b":2}'::json->'b' |
->> | int | Get JSON array element as text | '[1,2,3]'::json->>2 |
->> | text | Get JSON object field as text | '{"a":1,"b":2}'::json->>'b' |
#> | array of text | Get JSON object at specified path | '{"a":[1,2,3],"b":[4,5,6]}'::json#>'{a,2}' |
#>> | array of text | Get JSON object at specified path as text | '{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}' |
Table 9-40 shows the functions that are available for creating and manipulating JSON (see Section 8.14) data.
Table 9-40. JSON Support Functions
Function | Return Type | Description | Example | Example Result |
---|---|---|---|---|
array_to_json(anyarray [, pretty_bool]) | json | Returns the array as JSON. 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]) | json | Returns the row as JSON. Line feeds will be added between level 1 elements if pretty_bool is true. | row_to_json(row(1,'foo')) | {"f1":1,"f2":"foo"} |
to_json(anyelement) | json | Returns the value as JSON. If the data type is not builtin, and there is a cast from the type to json, the cast function will be used to perform the conversion. Otherwise, for any value other than a number, a boolean or NULL, the text representation will be used, escaped and quoted so that it is legal JSON. | to_json('Fred said "Hi."'::text) | "Fred said \"Hi.\"" |
json_array_length(json) | 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) | SETOF key text, value json | 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(from_json json) | SETOF key text, value text | Expands the outermost json object into a set of key/value pairs. The returned value 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[]) | json | Returns json object pointed to by path_elems. | 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[]) | text | Returns json object pointed to by path_elems. | json_extract_path_text('{"f2":{"f3":1},"f4":{"f5":99,"f6":"foo"}}','f4', 'f6') | foo |
json_object_keys(json) | SETOF text | Returns set of keys in the json object. Only the "outer" object will be displayed. | json_object_keys('{"f1":"abc","f2":{"f3":"a", "f4":"b"}}') | json_object_keys ------------------ f1 f2 |
json_populate_record(base anyelement, from_json json, [, use_json_as_text bool=false] | anyelement | Expands the object in from_json to a row whose columns match the record type defined by base. Conversion will be best effort; columns in base with no corresponding key in from_json will be left null. A column may only be specified once. | select * from json_populate_record(null::x, '{"a":1,"b":2}') | a | b ---+--- 1 | 2 |
json_populate_recordset(base anyelement, from_json json, [, use_json_as_text bool=false] | SETOF anyelement | Expands the outermost set of objects in from_json to a set whose columns match the record type defined by base. Conversion will be best effort; columns in base with no corresponding key in from_json will be left null. A column may only be specified once. | select * from json_populate_recordset(null::x, '[{"a":1,"b":2},{"a":3,"b":4}]') | a | b ---+--- 1 | 2 3 | 4 |
json_array_elements(json) | SETOF json | Expands a json array to a set of json elements. | json_array_elements('[1,true, [2,false]]') | value ----------- 1 true [2,false] |
Note: The hstore extension has a cast from hstore to json, so that converted hstore values are represented as json objects, not as string values.
See also Section 9.20 about the aggregate
function json_agg
which aggregates record
values as json efficiently.