9.15. JSON函式及運算子

Table 9.43shows the operators that are available for use with the two JSON data types (seeSection 8.14).

Table 9.43. jsonandjsonbOperators

Operator

Right Operand Type

Description

Example

Example Result

->

int

Get JSON array element (indexed from zero, negative integers count from the end)

'[{"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 astext

'[1,2,3]'::json->>2

3

->>

text

Get JSON object field astext

'{"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 astext

'{"a":[1,2,3],"b":[4,5,6]}'::json#>>'{a,2}'

3

Note

There are parallel variants of these operators for both thejsonandjsonbtypes. The field/element/path extraction operators return the same type as their left-hand input (eitherjsonorjsonb), except for those specified as returningtext, 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 field/element/path extraction operators that accept integer JSON array subscripts all support negative subscripting from the end of arrays.

The standard comparison operators shown inTable 9.1are available forjsonb, but not forjson. They follow the ordering rules for B-tree operations outlined atSection 8.14.4.

Some further operators also exist only forjsonb, as shown inTable 9.44. Many of these operators can be indexed byjsonboperator classes. For a full description ofjsonbcontainment and existence semantics, seeSection 8.14.3.Section 8.14.4describes how these operators can be used to effectively indexjsonbdata.

Table 9.44. AdditionaljsonbOperators

Operator

Right Operand Type

Description

Example

@>

jsonb

Does the left JSON value contain the right JSON path/value entries at the top level?

'{"a":1, "b":2}'::jsonb @> '{"b":2}'::jsonb

<@

jsonb

Are the left JSON path/value entries contained at the top level within the right JSON value?

'{"b":2}'::jsonb <@ '{"a":1, "b":2}'::jsonb

?

text

Does the_string_exist as a top-level key within the JSON value?

'{"a":1, "b":2}'::jsonb ? 'b'

`?

`

text[]

Do any of these array_strings_exist as top-level keys?

`'{"a":1, "b":2, "c":3}'::jsonb ?

array['b', 'c']`

?&

text[]

Do all of these array_strings_exist as top-level keys?

'["a", "b"]'::jsonb ?& array['a', 'b']

`

`

jsonb

Concatenate twojsonbvalues into a newjsonbvalue

`'["a", "b"]'::jsonb

'["c", "d"]'::jsonb`

-

text

Delete key/value pair or_string_element from left operand. Key/value pairs are matched based on their key value.

'{"a": "b"}'::jsonb - 'a'

-

text[]

Delete multiple key/value pairs or_string_elements from left operand. Key/value pairs are matched based on their key value.

'{"a": "b", "c": "d"}'::jsonb - '{a,c}'::text[]

-

integer

Delete the array element with specified index (Negative integers count from the end). Throws an error if top level container is not an array.

'["a", "b"]'::jsonb - 1

#-

text[]

Delete the field or element with specified path (for JSON arrays, negative integers count from the end)

'["a", {"b":1}]'::jsonb #- '{1,b}'

Note

The||operator concatenates the elements at the top level of each of its operands. It does not operate recursively. For example, if both operands are objects with a common key field name, the value of the field in the result will just be the value from the right hand operand.

Table 9.45shows the functions that are available for creatingjsonandjsonbvalues. (There are no equivalent functions forjsonb, of therow_to_jsonandarray_to_jsonfunctions. However, theto_jsonbfunction supplies much the same functionality as these functions would.)

Table 9.45. JSON Creation Functions

Function

Description

Example

Example Result

to_json(anyelement)to_jsonb(anyelement)

Returns the value asjsonorjsonb. Arrays and composites are converted (recursively) to arrays and objects; otherwise, if there is a cast from the type tojson, the cast function will be used to perform the conversion; otherwise, a scalar value is produced. For any scalar type other than a number, a Boolean, or a null value, the text representation will be used, in such a fashion that it is a validjsonorjsonbvalue.

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")jsonb_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")jsonb_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[])jsonb_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[])jsonb_object(keys text[], values text[])

This form ofjson_objecttakes 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

Thehstoreextension has a cast fromhstoretojson, so thathstorevalues converted via the JSON creation functions will be represented as JSON objects, not as primitive string values.

Table 9.46shows the functions that are available for processingjsonandjsonbvalues.

Table 9.46. 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 jsonsetof 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 typetext.

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[])

jsonjsonb

Returns JSON value pointed to bypath_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_astext(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 infrom_json_to a row whose columns match the record type defined bybase_(see note below).

select * from json_populate_record(null::myrowtype, '{"a": 1, "b": ["2", "a b"], "c": {"d": 4, "e": "a b c"}}')

a | b | c---+-----------+------------- 1 | {2,"a b"} | (4,"a b c")

json_populate_recordset(base anyelement, from_json json)jsonb_populate_recordset(base anyelement, from_json jsonb)

setof anyelement

Expands the outermost array of objects infrom_json_to a set of rows whose columns match the record type defined bybase_(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 jsonsetof 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 oftextvalues.

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 areobject,array,string,number,boolean, andnull.

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 returningrecord, the caller must explicitly define the structure of the record with anASclause.

select * from json_to_record('{"a":1,"b":[1,2,3],"c":[1,2,3],"e":"bar","r": {"a": 123, "b": "a b c"}}') as x(a int, b text, c int[], d text, r myrowtype)

a | b | c | d | r---+---------+---------+---+--------------- 1 | [1,2,3] | {1,2,3} | | (123,"a b c")

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 returningrecord, the caller must explicitly define the structure of the record with anASclause.

select * from json_to_recordset('[{"a":1,"b":"foo"},{"a":"2","c":"bar"}]') as x(a int, b text);

a | b---+----- 1 | foo 2 |

json_strip_nulls(from_json json)jsonb_strip_nulls(from_json jsonb)

jsonjsonb

Returns_from_json_with all object fields that have null values omitted. Other null values are untouched.

json_strip_nulls('[{"f1":1,"f2":null},2,null,3]')

[{"f1":1},2,null,3]

jsonb_set(target jsonb, path text[], new_value jsonb[,create_missingboolean])

jsonb

Returnstarget_with the section designated bypathreplaced bynew_value, or withnew_valueadded ifcreate_missingis true ( default istrue) and the item designated bypathdoes not exist. As with the path orientated operators, negative integers that appear inpath_count from the end of JSON arrays.

jsonb_set('[{"f1":1,"f2":null},2,null,3]', '{0,f1}','[2,3,4]', false)jsonb_set('[{"f1":1,"f2":null},2]', '{0,f3}','[2,3,4]')

[{"f1":[2,3,4],"f2":null},2,null,3][{"f1": 1, "f2": null, "f3": [2, 3, 4]}, 2]

jsonb_insert(target jsonb, path text[], new_value jsonb, [insert_afterboolean])

jsonb

Returnstarget_withnew_valueinserted. Iftargetsection designated bypathis in a JSONB array,new_valuewill be inserted before target or after ifinsert_afteris true (default isfalse). Iftargetsection designated bypathis in JSONB object,new_valuewill be inserted only iftargetdoes not exist. As with the path orientated operators, negative integers that appear inpath_count from the end of JSON arrays.

jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"')jsonb_insert('{"a": [0,1,2]}', '{a, 1}', '"new_value"', true)

{"a": [0, "new_value", 1, 2]}{"a": [0, 1, "new_value", 2]}

jsonb_pretty(from_json jsonb)

text

Returns_from_json_as indented JSON text.

jsonb_pretty('[{"f1":1,"f2":null},2,null,3]')

[ { "f1": 1, "f2": null }, 2, null, 3]

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 typejsonb, because the conversion was already done; but forjsoninput, this may result in throwing an error, as noted inSection 8.14.

Note

Injson_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

All the items of thepathparameter ofjsonb_setas well asjsonb_insertexcept the last item must be present in thetarget. Ifcreate_missingis false, all items of thepathparameter ofjsonb_setmust be present. If these conditions are not met thetargetis returned unchanged.

If the last path item is an object key, it will be created if it is absent and given the new value. If the last path item is an array index, if it is positive the item to set is found by counting from the left, and if negative by counting from the right --1designates the rightmost element, and so on. If the item is out of the range -array_length .. array_length -1, and create_missing is true, the new value is added at the beginning of the array if the item is negative, and at the end of the array if it is positive.

Note

Thejson_typeoffunction'snullreturn value should not be confused with a SQL NULL. While callingjson_typeof('null'::json)will returnnull, callingjson_typeof(NULL::json)will return a SQL NULL.

Note

If the argument tojson_strip_nullscontains duplicate field names in any object, the result could be semantically somewhat different, depending on the order in which they occur. This is not an issue forjsonb_strip_nullssincejsonbvalues never have duplicate object field names.

See alsoSection 9.20for the aggregate functionjson_aggwhich aggregates record values as JSON, and the aggregate functionjson_object_aggwhich aggregates pairs of values into a JSON object, and theirjsonbequivalents,jsonb_aggandjsonb_object_agg.