Authors
Forward Xu, Jark Wu
Status
Current state: "Under Discussion"
Discussion thread: http://apache-flink-mailing-list-archive.1008284.n3.nabble.com/DISCUSS-Support-JSON-functions-in-Flink-SQL-td32674.html
JIRA: here (<- link to https://issues.apache.org/jira/browse/FLINK-XXXX)
Released: <Flink Version>
Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).
Motivation
Currently, Flink SQL does not support the SQL 2016 JSON function. and many of the message middleware data are in JSON format. For example: Kafka, Flink SQL can support JSON operation to more easily parse the data in Kafka. In addition, the data in some relational databases is also stored and ingested in JSON format.
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The ARRAY WRAPPER clause defines how to represent a JSON array result in JSON_QUERY function. The following examples compare the wrapper behaviors.
Use in TableApi:
jsonExists
JAVA/PYTHON/SCALA | DESCRIPTION |
STRING.jsonExists(path) | Whether a jsonValue satisfies a search criterion described using JSON path expression path. |
STRING.jsonExists(path |
,JsonErrorStrategy.ERROR) | JsonErrorStrategy.ERROR means ERROR ON ERROR. |
STRING.jsonExists(path,JsonErrorStrategy.UNKNOWN) | JsonErrorStrategy.UNKNOWN means UNKNOWN ON ERROR. |
jsonValue
JAVA/PYTHON/SCALA | DESCRIPTION |
STRING.jsonValue(path) | Extract an SQL scalar from a jsonValue using JSON path expression |
path |
. |
STRING. |
jsonValue(path,JsonReturningStrategy.INTEGER) |
JsonReturningStrategy is an enum object that can be integer, boolean, etc. | |
STRING.jsonValue(path,JsonEmptyStrategy.NULL) | JsonEmptyStrategy.NULL means NULL ON EMPTY. |
STRING.jsonValue(path,JsonEmptyStrategy.ERROR) | JsonEmptyStrategy.ERROR means ERROR ON EMPTY. |
STRING.jsonValue(path,JsonEmptyStrategy.DEFAULT) | JsonEmptyStrategy.DEFAULT means DEFAULT ON EMPTY. |
STRING.jsonValue(path,JsonErrorStrategy.NULL) | JsonEmptyStrategy.NULL means NULL ON ERROR. |
STRING.jsonValue(path,JsonErrorStrategy.ERROR) | JsonEmptyStrategy.ERROR means NULL ON ERROR. |
STRING.jsonValue(path,JsonErrorStrategy.DEFAULT) | JsonEmptyStrategy.DEFAULT means NULL ON ERROR. |
jsonQuery
JAVA/PYTHON/SCALA | DESCRIPTION |
STRING.jsonQuery(path) | Extract a JSON object or JSON array from jsonValue using the path JSON path expression. |
STRING.jsonQuery(path,JsonEmptyStrategy.NULL) | JsonEmptyStrategy.NULL means NULL ON EMPTY. |
STRING.jsonQuery(path,JsonEmptyStrategy.ERROR) | JsonEmptyStrategy.ERROR means ERROR ON EMPTY. |
STRING.jsonQuery(path,JsonEmptyStrategy.EMPTY_ARRAY) | JsonEmptyStrategy.EMPTY_ARRAY means EMPTY ARRAY ON EMPTY. |
STRING.jsonQuery(path,JsonEmptyStrategy.EMPTY_OBJECT) | JsonEmptyStrategy.EMPTY_OBJECT means EMPTY OBJECT ON EMPTY. |
STRING.jsonQuery(path,JsonErrorStrategy.NULL) | JsonEmptyStrategy.NULL means NULL ON ERROR. |
STRING.jsonQuery(path,JsonErrorStrategy.ERROR) | JsonEmptyStrategy.ERROR means NULL ON ERROR. |
STRING.jsonQuery(path,JsonErrorStrategy.EMPTY_ARRAY) | JsonErrorStrategy.EMPTY_ARRAY means EMPTY ARRAY ON ERROR. |
STRING.jsonQuery(path,JsonErrorStrategy.EMPTY_OBJECT) | JsonErrorStrategy.EMPTY_OBJECT means EMPTY OBJECT ON ERROR. |
STRING.jsonQuery(path,JsonWrapperStrategy.NONE) | JsonWrapperStrategy.NONE means WITHOUT WRAPPER |
STRING.jsonQuery(path,JsonWrapperStrategy.NONE_ARRAY) | JsonWrapperStrategy.NONE_ARRAY means WITHOUT WRAPPER |
STRING.jsonQuery(path,JsonWrapperStrategy.DEFAULT) | JsonWrapperStrategy.DEFAULT means WITH WRAPPER |
Example Data:
{"a": "[1,2]", "b": [1,2], "c": "hi"} |
Comparison:
OPERATOR | $.A | $.B | $.C |
JSON_EXISTS | true | true | true |
JSON_VALUE | [1, 2] | error | hi |
JSON QUERY WITHOUT ARRAY WRAPPER | error | [1, 2] | error |
JSON QUERY WITH UNCONDITIONAL ARRAY WRAPPER | [ “[1,2]” ] | [ [1,2] ] | [ “hi” ] |
JSON QUERY WITH CONDITIONAL ARRAY WRAPPER | [ “[1,2]” ] | [1,2] | [ “hi” ] |
Constructor Functions
Use in SQL:
SQL SYNTAX | DESCRIPTION |
JSON_OBJECT( { [ KEY ] name VALUE value [ FORMAT JSON ] | name : value [ FORMAT JSON ] } * [ { NULL | ABSENT } ON NULL ] ) | Construct JSON object using a series of key (name) value (value) pairs. |
JSON_OBJECTAGG( { [ KEY ] name VALUE value [ FORMAT JSON ] | name : value [ FORMAT JSON ] } [ { NULL | ABSENT } ON NULL ] ) | Aggregate function to construct a JSON object using a key (name) value (value) pair. |
JSON_ARRAY( { value [ FORMAT JSON ] } * [ { NULL | ABSENT } ON NULL ] ) | Construct a JSON array using a series of values (value). |
JSON_ARRAYAGG( value [ FORMAT JSON ] [ ORDER BY orderItem [, orderItem ]* ] [ { NULL | ABSENT } ON NULL ] ) |
Aggregate function to construct a JSON array using a value (value). |
Use in TableApi:
jsonObject
JAVA/PYTHON/SCALA | DESCRIPTION |
jsonObject(ANY1, ANY2, ...) | Construct JSON object using a series of |
JSON_ARRAYAGG( value [ FORMAT JSON ] [ ORDER BY orderItem [, orderItem ]* ] [ { NULL | ABSENT } ON NULL ] )
Aggregate function to construct a JSON array using a value (value).
key (name) value (value) pairs.Table API currently only supports JSON string operations. | |
jsonObject(ANY1, ANY2, …,JsonNullStrategy.NULL) | JsonNullStrategy.NULL means NULL ON NULL |
jsonObject(ANY1, ANY2, …,JsonNullStrategy.ABSENT) | JsonNullStrategy.ABSENT means ABSENT ON NULL |
jsonObject(ANY1, ANY2, …,JsonFormatStrategy.TRUE) | JsonFormatStrategy.TRUE means FORMAT JSON |
jsonObjectAggUse in TableApi:
JAVA/PYTHON/SCALA | DESCRIPTION |
jsonObjectAgg(ANY1, |
ANY2) |
Aggregate function to construct a JSON object using a |
key (name) value (value) |
pair.Table API currently only |
supports JSON string operations. | |
jsonObjectAgg(ANY1, ANY2,JsonNullStrategy.NULL) | JsonNullStrategy.NULL means NULL ON NULL |
jsonObjectAgg(ANY1, ANY2,,JsonNullStrategy.ABSENT) | JsonNullStrategy.ABSENT means ABSENT ON NULL |
jsonObjectAgg(ANY1, ANY2,,JsonFormatStrategy.TRUE) | JsonFormatStrategy.TRUE means FORMAT JSON |
jsonArray
JAVA/PYTHON/SCALA | DESCRIPTION |
jsonArray(ANY1, ANY2, ...) |
Construct a JSON |
array using a |
series of values (value) |
. Table API currently only supports JSON string operations. | |
jsonArray(ANY1, ANY2, …,JsonNullStrategy.NULL) | JsonNullStrategy.NULL means NULL ON NULL |
jsonArray(ANY1, ANY2, …,JsonNullStrategy.ABSENT) |
JsonNullStrategy.ABSENT means ABSENT ON NULL | |
jsonArray(ANY1, ANY2, …,JsonFormatStrategy.TRUE) | JsonFormatStrategy.TRUE means FORMAT JSON |
jsonArrayAgg
JAVA/PYTHON/SCALA | DESCRIPTION |
jsonArrayAgg(ANY) | Aggregate function to construct a JSON array using a value (value). Table API currently only supports JSON string operations. |
jsonArrayAgg(ANY,JsonNullStrategy.NULL) | JsonNullStrategy.NULL means NULL ON NULL |
jsonArrayAgg(ANY,JsonNullStrategy.ABSENT) | JsonNullStrategy.ABSENT means ABSENT ON NULL |
jsonArrayAgg(ANY,JsonFormatStrategy.TRUE) | JsonFormatStrategy.TRUE means FORMAT JSON |
Note: The flag FORMAT JSON indicates the value is formatted as JSON character string. When FORMAT JSON is used, the value should be de-parse from JSON character string to a SQL structured value.
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If ORDER BY clause is provided, JSON_ARRAYAGG sorts the input rows into the specified order before performing aggregation.
Comparison:
OPERATOR | RESULT |
JSON_OBJECT('id', 87, 'name', 'carrot') | {"id": 87, "name": "carrot"} |
JSON_ARRAY(1, "abc", NULL, TRUE) | [1, "abc", null, true] |
Simple Simple Data Table T1:
o_id | attribute | value |
2 | color | red |
2 | fabric | silk |
3 | color | green |
3 | shape | square |
SELECT o_id, JSON_OBJECTAGG(attribute, value) FROM t1 GROUP BY o_id;
OPERATOR | o_id | AFTER AGG |
JSON_OBJECTAGG(attribute, value) | 2 | {"color": "red", "fabric": "silk"} |
JSON_OBJECTAGG(attribute, value) | 3 | {"color": "green", "shape": "square"} |
SELECT o_id, JSON_ARRAYAGG(attribute) AS attributes FROM t1 GROUP BY o_id;
OPERATOR | o_id | AFTER AGG |
JSON_ARRAYAGG(attribute) | 2 | ["color", "fabric"] |
JSON_ARRAYAGG(attribute) | 3 | ["color", "shape"] |
Comparison Operators
Applications will frequently want to ensure that the data they expect to consume as JSON data is, indeed, JSON data. The IS JSON predicate determines whether the value of a specified string does or does not conform to the structural rules for JSON. The syntax of the IS JSON predicate is:
Use in SQL:
SQL SYNTAX | DESCRIPTION |
jsonValue IS JSON [ VALUE ] | Whether jsonValue is a JSON value.Table API functions currently only support JSON strings as input parameters. |
jsonValue IS NOT JSON [ VALUE ] | Whether jsonValue is not a JSON value.Table API functions currently only support JSON strings as input parameters. |
jsonValue IS JSON SCALAR | Whether jsonValue is a JSON scalar value.Table API functions currently only support JSON strings as input parameters. |
jsonValue IS NOT JSON SCALAR | Whether jsonValue is not a JSON scalar value.Table API functions currently only support JSON strings as input parameters. |
jsonValue IS JSON OBJECT | Whether jsonValue is a JSON object.Table API functions currently only support JSON strings as input parameters. |
jsonValue IS NOT JSON OBJECT | Whether jsonValue is not a JSON object.Table API functions currently only support JSON strings as input parameters. |
jsonValue IS JSON ARRAY | Whether jsonValue is a JSON array.Table API functions currently only support JSON strings as input parameters. |
jsonValue IS NOT JSON ARRAY | Whether jsonValue is not a JSON array.Table API functions currently only support JSON strings as input parameters. |
Use in TableApi:
JAVA/PYTHON/SCALA | DESCRIPTION |
ANY.isJsonValue() | Whether jsonValue is a JSON value.Table API functions currently only support JSON strings as input parameters. |
ANY.isNotJsonValue() | Whether jsonValue is not a JSON value.Table API functions currently only support JSON strings as input parameters. |
ANY.isJsonScalar() | Whether jsonValue is a JSON scalar value.Table API functions currently only support JSON strings as input parameters. |
ANY.isNotJsonScalar() | Whether jsonValue is not a JSON scalar value.Table API functions currently only support JSON strings as input parameters. |
ANY.isJsonObject() | Whether jsonValue is a JSON object.Table API functions currently only support JSON strings as input parameters. |
ANY.isNotJsonObject() | Whether jsonValue is not a JSON object.Table API functions currently only support JSON strings as input parameters. |
ANY.isJsonArray() | Whether jsonValue is a JSON array.Table API functions currently only support JSON strings as input parameters. |
ANY.isNotJsonArray() | Whether jsonValue is not a JSON array.Table API functions currently only support JSON strings as input parameters. |
The test example:
tester.checkBoolean("'{}' is json value", true); tester.checkBoolean("'{]' is json value", false); tester.checkBoolean("'{}' is json object", true); tester.checkBoolean("'[]' is json object", false); tester.checkBoolean("'{}' is json array", false); tester.checkBoolean("'[]' is json array", true); tester.checkBoolean("'100' is json scalar", true); tester.checkBoolean("'[]' is json scalar", false); tester.checkBoolean("'{}' is not json value", false); tester.checkBoolean("'{]' is not json value", true); tester.checkBoolean("'{}' is not json object", false); tester.checkBoolean("'[]' is not json object", true); tester.checkBoolean("'{}' is not json array", true); tester.checkBoolean("'[]' is not json array", false); tester.checkBoolean("'100' is not json scalar", false); tester.checkBoolean("'[]' is not json scalar", true); |
Implementation Details
Table Api interface proposal
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