Postgres 16

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CREATE TABLE tbl (
  id int
, product text
, cost numeric
);

INSERT INTO tbl VALUES
  (1, 'Phone' , 105)
, (2, 'Camera',  82)
, (3, 'Cup'   , 103)
, (4, NULL    , NULL)
, (5, NULL    ,  66)
, (6, 'foo'   , NULL)
;

CREATE TABLE



INSERT 0 6


SELECT percentile_disc('{0,.5,1}'::float[]) WITHIN GROUP (ORDER BY id     ) AS pctl_id
     , percentile_disc('{0,.5,1}'::float[]) WITHIN GROUP (ORDER BY product) AS pctl_product   
     , percentile_disc('{0,.5,1}'::float[]) WITHIN GROUP (ORDER BY cost   ) AS pctl_cost
FROM   tbl;


pctl_id
pctl_product
pctl_cost


{1,3,6}
{Camera,Cup,foo}
{66,82,105}



SELECT 1


-- only for big tables (can come up empty for small tables)
SELECT percentile_disc('{0,1}'::float[]) WITHIN GROUP (ORDER BY id) AS pctl_ids
     , percentile_disc('{0,1}'::float[]) WITHIN GROUP (ORDER BY product) pctl_product   
     , percentile_disc('{0,1}'::float[]) WITHIN GROUP (ORDER BY cost) AS pctl_cost
FROM   tbl TABLESAMPLE SYSTEM (10);


pctl_ids
pctl_product
pctl_cost


null
null
null



SELECT 1


SELECT percentile_disc('{0,1}'::float[]) WITHIN GROUP (ORDER BY id) AS pctl_ids
     , percentile_disc('{0,1}'::float[]) WITHIN GROUP (ORDER BY product) pctl_product   
     , percentile_disc('{0,1}'::float[]) WITHIN GROUP (ORDER BY cost) AS pctl_cost
FROM  (
   SELECT id, product, cost 
   FROM   tbl
   LIMIT  2
   ) sub;


pctl_ids
pctl_product
pctl_cost


{1,2}
{Camera,Phone}
{82,105}



SELECT 1


SELECT array_agg(id      ORDER BY id     ) AS ids
     , array_agg(product ORDER BY product) AS products
     , array_agg(cost    ORDER BY cost   ) AS costs
FROM  (
   SELECT id, product, cost 
   FROM   tbl
   -- no ORDER BY, take arbitrary rows cheaply
   LIMIT  5
   ) sub;


ids
products
costs


{1,2,3,4,5}
{Camera,Cup,Phone,NULL,NULL}
{66,82,103,105,NULL}



SELECT 1