CODEWITHSUNDEEP
sqlpostgresqlcase
ksevelyar
ksevelyar

Reputation: 342

Combine multiple rows to one after group by

UPDATE: https://www.db-fiddle.com/f/5fGUTSsAhGRPYPk33wDSzz/0

Sorry for asking the question very similar to the previous one, but I am really stuck here.

There are multiple tables:

Structure:

I am trying to add role fields to items, it should take role_type and it is value from items_zones and if it is NULL fetch fallback value from zone (roles_zones).

I started with:

SELECT 
    items.id,
    (z_roles.role_type_id) as z_role_type_id,
    (z_roles.id) as z_role_id,
    MAX(i_roles.role_type_id) as i_role_type_id,
    MAX(i_roles.id) as i_role_id
FROM 
    items
LEFT JOIN 
    zones as j_zones ON j_zones.id = items.zone_id
LEFT JOIN 
    roles_zones ON roles_zones.zone_id = j_zones.id
LEFT JOIN 
    roles as z_roles ON (z_roles.id = roles_zones.role_id)
LEFT JOIN 
    items_roles ON items_roles.item_id = items.id
LEFT JOIN 
    roles as i_roles ON items_roles.role_id = i_roles.id
                     AND (z_roles.role_type_id = i_roles.role_type_id)
WHERE 
    items.id = 834
GROUP BY
    items.id, z_roles.role_type_id, z_roles.id
ORDER BY 
    i_role_id;

Looks right:

id  |z_role_type_id |z_role_id |i_role_type_id |i_role_id |
----+---------------+----------+---------------+----------+
834 |5              |111       |5              |68        |
834 |11             |120       |11             |120       |
834 |7              |77        |               |          |
834 |2              |2         |               |          |
834 |12             |91        |               |          |
834 |4              |78        |               |          |
834 |8              |36        |               |          |

And now this query: 

SELECT
    items.id,
    z_roles.role_type_id as z_role_type_id,
    z_roles.id as z_role_id,
    MAX(i_roles.role_type_id) AS i_role_type_id,
    MAX(i_roles.id) AS i_role_id,
    MAX(CASE
           WHEN (i_roles.role_type_id = 5) THEN i_roles.id
           WHEN (z_roles.role_type_id = 5) THEN z_roles.id
        END) AS role_type_5_value,
    MAX(CASE
           WHEN (i_roles.role_type_id = 11) THEN i_roles.id
           WHEN (z_roles.role_type_id = 11) THEN z_roles.id
        END) AS role_type_11_value,
    MAX(CASE
           WHEN (i_roles.role_type_id = 7) THEN i_roles.id
           WHEN (z_roles.role_type_id = 7) THEN z_roles.id
        END) AS role_type_7_value
FROM 
    items
LEFT JOIN 
    zones AS j_zones ON j_zones.id = items.zone_id
LEFT JOIN 
    roles_zones ON roles_zones.zone_id = j_zones.id
LEFT JOIN 
    roles AS z_roles ON (z_roles.id = roles_zones.role_id)
LEFT JOIN 
    items_roles ON items_roles.item_id = items.id
LEFT JOIN 
    roles AS i_roles ON items_roles.role_id = i_roles.id
                     AND (z_roles.role_type_id = i_roles.role_type_id)
WHERE 
    items.id = 834
GROUP BY 
    items.id,
    z_roles.role_type_id,
    z_roles.id
ORDER BY 
    items.id, i_role_id;

Generates this:

 id  | z_role_type_id | z_role_id | i_role_type_id | i_role_id | role_type_5_value | role_type_11_value | role_type_7_value 
-----+----------------+-----------+----------------+-----------+-------------------+--------------------+-------------------
 834 |              5 |       111 |              5 |        68 |               111 |                    |                  
 834 |             11 |       120 |             11 |       120 |                   |                120 |                  
 834 |              7 |        77 |                |           |                   |                    |                77
 834 |              2 |         2 |                |           |                   |                    |                  
 834 |             12 |        91 |                |           |                   |                    |                  
 834 |              4 |        78 |                |           |                   |                    |                  
 834 |              8 |        36 |                |           |                   |                    |                  
(7 rows)

Multiple rows and wrong value for role_type_5_value. Probably because of MAX aggregator. Is it possible to use something like first aggregator (because rows ordered by i_role_id and first results are right)?

I want this:

 id  | role_type_5_value | role_type_11_value | role_type_7_value 
-----+-------------------+--------------------+-------------------
 834 |                68 |                120 |                77

I tried to group by by aggregated fields, (role_type_5_value, role_type_11_value, role_type_7_value) but this is simply not working.

Upvotes: 1

Views: 62

Answers (1)

wildplasser
wildplasser

Reputation: 44230

First: removing the unneeded bridge-tables from the main query and squeeze them into EXISTS() terms will simplify your query.(you only need three tables, the rest is glue)

Second: don't put all your terms in the GROUP BY clause.

SELECT
  i0.id
   , MAX(CASE
    WHEN (r1.role_type_id = 5) THEN r1.id
    WHEN (r0.role_type_id = 5) THEN r0.id
  END) AS role_type_5_value
  , MAX(CASE
    WHEN (r1.role_type_id = 11) THEN r1.id
    WHEN (r0.role_type_id = 11) THEN r0.id
  END) AS role_type_11_value
  , MAX(CASE
    WHEN (r1.role_type_id = 7) THEN r1.id
    WHEN (r0.role_type_id = 7) THEN r0.id
  END) AS role_type_7_value

FROM items i0
LEFT JOIN roles AS r0
  ON EXISTS ( SELECT*
        FROM zones AS z0
        JOIN roles_zones rz ON rz.zone_id = z0.id
        WHERE z0.id = i0.zone_id
        AND r0.id = rz.role_id)

LEFT JOIN roles AS r1
  ON EXISTS ( SELECT*
        FROM items_roles ir
        WHERE ir.item_id = i0.id
        AND ir.role_id = r1.id
        AND r0.role_type_id = r1.role_type_id
        )

WHERE i0.id = 834
GROUP BY i0.id
         -- r0.role_type_id,
         -- r0.id
ORDER BY i0.id;

Upvotes: 1

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