Oracle 23c

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select * from V$VERSION;

BANNER	BANNER_FULL	BANNER_LEGACY	CON_ID
Oracle Database 23c Free, Release 23.0.0.0.0 - Developer-Release	Oracle Database 23c Free, Release 23.0.0.0.0 - Developer-Release Version 23.2.0.0.0	Oracle Database 23c Free, Release 23.0.0.0.0 - Developer-Release	0

with tbltmp(x, y) as (

select * from (

VALUES

(5215, 57),

(18943, 221),

(18943, 230),

(18943, 238),

(21488, 257),

(21488, 270),

(5215, 67),

(5215, 77),

(5215, 87),

(5215, 97)

) as t(x, y)

rtbltmp as (

select d.*,

dense_rank() over(order by x) as rnx,

row_number() over(partition by x order by y) as rny,

count(y) over(partition by x) as cnt

from tbltmp d

)

, solution(x,y, rnx, rny, js) as (

select x,y, rnx, rny, '[' || x || ',' || y || ']'

from rtbltmp

where rnx = 1

union all

select d.x, d.y, d.rnx, d.rny,

r.js || ',[' || d.x || ',' || d.y || ']'

from solution r

join rtbltmp d

(d.rnx = r.rnx + 1)