Double flattening of arrays. Ksqldb 0.8.1 - apache-kafka

Question

DATA.
kafkacat -b 127.0.0.1 -t group-topic -P
{"groups":[{"name":"Roberth","surname":"Smith","origin":"England","albums":["Wish","Desintegration"],"group":"The Cure"},{"name":"Peter","surname":"Murphy","origin":"England","albums":["Mask","In The Flat Field"],"group":"Bauhaus"}]};
// STRUCTURE STREAM
SET 'auto.offset.reset' = 'earliest';
CREATE STREAM GROUPS_01
(groups ARRAY<STRUCT<
albums ARRAY<VARCHAR>,
name VARCHAR,
surname VARCHAR
>>)
WITH (kafka_topic='group-topic', value_format='JSON');
SELECT
EXPLODE(groups)->name AS name,
EXPLODE(groups)->surname AS surname,
EXPLODE(groups)->albums AS albums
FROM GROUPS_01
EMIT CHANGES;
// I have
NAME SURNAME ALBUMS
Roberth Smith [Wish,Desintegration]
Peter Murphy [Mask,In The Flat Field]
// I need
NAME SURNAME ALBUM
Roberth Smith Wish
Roberth Smith Desintegration
Peter Murphy Mask
Peter Murphy In The Flat Field
// TRY
EXPLODE(groups)->EXPLODE(albums)->album AS album
EXPLODE(albums)->album AS album

Answer 1

For clarity, here's the source data you provided:
{
"groups": [
{
"name": "Roberth",
"surname": "Smith",
"origin": "England",
"albums": [
"Wish",
"Desintegration"
],
"group": "The Cure"
},
{
"name": "Peter",
"surname": "Murphy",
"origin": "England",
"albums": [
"Mask",
"In The Flat Field"
],
"group": "Bauhaus"
}
]
}
First explode out the root array
ksql> CREATE STREAM EX1A AS SELECT EXPLODE(GROUPS) AS GROUP_SINGLE FROM GROUPS_01 EMIT CHANGES;
Message
-----------------------------------
Created query with ID CSAS_EX1A_5
-----------------------------------
This gives us :
ksql> SELECT * FROM EX1A EMIT CHANGES;
+----------------+-------+-----------------------------------------------------------+
|ROWTIME |ROWKEY |GROUP_SINGLE |
+----------------+-------+-----------------------------------------------------------+
|1585666857714 |null |{ALBUMS=[Wish, Desintegration], NAME=Roberth, SURNAME=Smith|
| | |} |
|1585666857714 |null |{ALBUMS=[Mask, In The Flat Field], NAME=Peter, SURNAME=Murp|
| | |hy} |
Now use the -> operator to access the nested structure and explode the ALBUMS array:
CREATE STREAM ALBUMS_EXPLODED AS
SELECT GROUP_SINGLE->NAME AS NAME,
GROUP_SINGLE->SURNAME AS SURNAME,
EXPLODE(GROUP_SINGLE->ALBUMS) AS ALBUM
FROM EX1A
EMIT CHANGES;
ksql> SELECT NAME, SURNAME, ALBUM FROM ALBUMS_EXPLODED EMIT CHANGES;
+-------------------+----------------------+-------------------+
|NAME |SURNAME |ALBUM |
+-------------------+----------------------+-------------------+
|Roberth |Smith |Wish |
|Roberth |Smith |Desintegration |
|Peter |Murphy |Mask |
|Peter |Murphy |In The Flat Field |