Get array of records based on two keys in same table

Question

I have tried this on the following table,

SELECT DISTINCT
  a.main_id,
 array_agg(distinct a.secondary_id )  AS arr                    
FROM table1 a JOIN table1 b ON a.secondary_id = b.secondary_id or a.tertiary_id = b.tertiary_id
group by a.main_id, a.secondary_id , b.tertiary_id

I added the distinct to omit the duplicates But I can not get the whole row as an element in the array which does not even put the rows together to the array based on the below mentioned requirement. I was following this.

Table script:

 Create table table1 
(  
   id bigserial NOT NULL,
   main_id integer NOT NULL,
   secondary_id integer,
   tertiary_id integer,
   data1 text,
   data2 text,
   CONSTRAINT table1_pk PRIMARY KEY (main_id)

)

Data:

INSERT INTO table1(
             main_id, secondary_id, tertiary_id, data1, data2)
    VALUES (1,2,NULL,'data1_1_2_N','data2_1_2_N'),
       (2,2,NULL,'data1_2_2_N','data2_2_2_N'),
       (3,3,5,'data1_3_3_5','data2_3_3_5'),
       (4,3,5,'data1_4_3_5','data2_4_3_5'),
       (5,NULL,1,'data1_5_N_1','data2_5_N_1'),
       (6,NULL,1,'data1_6_N_1','data2_6_N_1'),
       (7,NULL,1,'data1_7_N_1','data2_7_N_1'),
       (8,NULL,2,'data1_8_N_2','data2_8_N_2'),
       (9,NULL,2,'data1_9_N_2','data2_9_N_2'),
       (10,NULL,3,'data1_10_N_3','data2_10_N_3'),
       (11,12,12,'data1_11_12_12','data2_11_12_12'),
       (12,12,11,'data1_12_12_11','data2_12_12_11')

Requirement:

If secondary_id is equal in two or more rows they should be considered as one set, else if tertiary_id is equal they can be considered as one set.

Expected Result:

   1 | {(1,2,NULL,'data1_1_2_N','data2_1_2_N'),(2,2,NULL,'data1_2_2_N','data2_2_2_N')}
   2 | {(3,3,NULL,'data1_3_3_N','data2_3_3_N'),(4,3,NULL,'data1_4_3_N','data2_4_3_N')}
   3 | {(5,NULL,1,'data1_5_N_1','data2_5_N_1'),(6,NULL,1,'data1_6_N_1','data2_6_N_1'),(7,NULL,1,'data1_7_N_1','data2_7_N_1')}
   4 | {(8,NULL,2,'data1_8_N_2','data2_8_N_2'),(9,NULL,2,'data1_9_N_2','data2_9_N_2')}
   5 | {(10,NULL,3,'data1_10_N_3','data2_10_N_3')}
   6 | {(11,12,12,'data1_11_12_12','data2_11_12_12'),(12,12,11,'data1_12_12_11','data2_12_12_11') }

Version "PostgreSQL 9.3.11"

Remove `DISTINCT a.main_id,` from `select`, remove `a.main_id,` from `group by`, change `array_agg(distinct a.secondary_id)` to `array_agg(distinct a.*)` - then you will get something like you want. — Abelisto, Aug 26 '16 at 19:24
@Abelisto Your query works fine except one scenario.. when same id appears in both `secondary_id` and `tertiary_id`. eg: main_id 11 and 12 duplicate. All the others are fine — Marlon Abeykoon, Aug 27 '16 at 03:34
@MarlonAbeykoon why don't you have main_id 11 and 12 in your expected output? — Kamil Gosciminski, Aug 27 '16 at 03:44

score 1 · Accepted Answer · answered Aug 27 '16 at 04:06

This should achieve your output. The trick sticks within conditional group by clause to handle cases where secondary_id and tertiary_id are the same for a record which has a matching record on both of those fields.

select array_agg(distinct t1) 
from table1 t1 
join table1 t2 on 
  t1.secondary_id = t2.secondary_id 
  or t1.tertiary_id = t2.tertiary_id 
group by
  case 
    when t1.secondary_id is null or t1.secondary_id is null 
      then concat(t1.secondary_id,'#',t1.tertiary_id) -- #1
    when t1.secondary_id is not null and t1.tertiary_id is not null and t1.secondary_id = t2.secondary_id 
      then t1.secondary_id::TEXT -- #2
    when t1.secondary_id is not null and t1.tertiary_id is not null and t1.tertiary_id = t2.tertiary_id 
      then t1.tertiary_id::TEXT -- #3
    end 
order by 1

Standard case is when any of the fields are null, which stands for #1. We need to group by both columns and we're tricking it by concatenating both values from columns with a # mark and doing a group by this concatenated column.

For #2 and #3 we need to cast the grouping value to type text to make it go through (types returned by CASE statement need to be the same).

Option #2 serves the case when both values are not null and secondary_id matches between those "chosen" rows from selfjoin. Option #3 is analogical, but for tertiary_id match.

Output:

                                                 array_agg
------------------------------------------------------------------------------------------------------------
 {"(1,1,2,,data1_1_2_N,data2_1_2_N)","(2,2,2,,data1_2_2_N,data2_2_2_N)"}
 {"(3,3,3,5,data1_3_3_5,data2_3_3_5)","(4,4,3,5,data1_4_3_5,data2_4_3_5)"}
 {"(5,5,,1,data1_5_N_1,data2_5_N_1)","(6,6,,1,data1_6_N_1,data2_6_N_1)","(7,7,,1,data1_7_N_1,data2_7_N_1)"}
 {"(8,8,,2,data1_8_N_2,data2_8_N_2)","(9,9,,2,data1_9_N_2,data2_9_N_2)"}
 {"(10,10,,3,data1_10_N_3,data2_10_N_3)"}
 {"(11,11,4,4,data1_11_4_4,data2_11_4_4)","(12,12,4,11,data1_12_4_11,data2_12_4_11)"}

If you'd like to get rid of column id from your record, you could use a CTE and select all columns but id and then refer to that CTE in from clause.

Thanks for the answer and explanation +1 – Marlon Abeykoon Aug 28 '16 at 15:30 — Marlon Abeykoon, Aug 28 '16 at 15:30

Get array of records based on two keys in same table

1 Answers1