Oracle and PostgreSQL – Constructing Set-Based Query for Subset Problem

oraclepostgresql

I have a DB of the following structure (picture shows simplified version)

enter image description here

How should I construct a query to get only those recipees, that can be cooked, i.e. for each ingredient in a receipe requiredQuaintity > availableQuantity?

I tried this:

SELECT r.Name
FROM
   Receipe r
   JOIN RecipeIngredients ri ON ri.RecipeID = r.Id
   JOIN Ingredients i ON i.ID = ri.IngredientsId
WHERE
   ri.RequiredQuantity - i.AvailableQuantity > 0

but am not sure this is correct as I think this will only return available ingredients. How should I modify above query to produce only receipees where each of ingredient is available?
Thank you for help

—- Edit —-

Maybe something like this:

SELECT r.Name
FROM
(
    SELECT   r.Name AS Name
             r.Id AS Id
           , CASE (
                WHEN (ri.RequiredQuantity - i.AvailableQuantity >= 0)
                THEN 1
             ) AS Available
    FROM
       Receipe r
       JOIN RecipeIngredients ri ON ri.RecipeID = r.Id
       JOIN Ingredients i ON i.ID = ri.IngredientsId
    WHERE
           ri.RequiredQuantity - i.AvailableQuantity >= 0  
    GROUP BY
       r.Id
) AS results
WHERE
    // count of ingredients with value 1 for each recipe == count of all required ingredients for this recipe

Best Answer

Assuming referential integrity and all columns to be NOT NULL, this should be simplest and fastest:

SELECT *
FROM   Receipe r
WHERE  NOT EXISTS (
   SELECT 1
   FROM   Ingredients i
   JOIN   RecipeIngredients ON ri.IngredientsId = i.ID
   WHERE  ri.RecipeID = r.Id
   AND    ri.RequiredQuantity > i.AvailableQuantity
   );

Basically, use a NOT EXISTS anti-semi-join to rule out recipes with any shortcomings. As soon as the first is found, Postgres can drop the recipe at hand from the result and move on.

Aside: My standing advice is not to use CaMeL-case identifiers in Postgres.

Related Solutions

Postgresql – Problem with permissions for user

GRANTing ALL permissions for public to the database is mostly redundant (as public has connect, temporary by default, so you'd only be adding CREATE which you probably don't want to do). You probably expected a GRANT ALL on the database to result in a recursive GRANT ALL to contained schemas and tables. GRANT is not recursive, so this doesn't happen; a GRANT ALL on a database just grants CONNECT and TEMPORARY rights to the database, with no effect on contained schemas and tables.

The default GRANTs are, from the docs on GRANT:

PostgreSQL grants default privileges on some types of objects to PUBLIC. No privileges are granted to PUBLIC by default on tables, columns, schemas or tablespaces. For other types, the default privileges granted to PUBLIC are as follows: CONNECT and CREATE TEMP TABLE for databases; EXECUTE privilege for functions; and USAGE privilege for languages. The object owner can, of course, REVOKE both default and expressly granted privileges. (For maximum security, issue the REVOKE in the same transaction that creates the object; then there is no window in which another user can use the object.) Also, these initial default privilege settings can be changed using the ALTER DEFAULT PRIVILEGES command.

So you can see you don't need to GRANT anything on the database unless you want the user to be able to create schemas, etc. You need to:

GRANT USAGE ON SCHEMA myschema TO theuser; for any schema other than public. CREATE can be granted if you want the user to be able to make tables, views, etc.
GRANT SELECT, INSERT, UPDATE, DELETE ON TABLE sometable TO theuser; for tables. I've omitted the TRUNATE, REFERENCES and TRIGGER rights as you probably don't want to grant them.
GRANT USAGE ON SEQUENCE sometable_somecolumn_seq TO theuser; for any sequences that are used in table defaults, either explicitly or via a SERIAL or BIGSERIAL column.

... etc. See the manual for GRANT linked above for full definitions of what the privileges do, which are available on which objects, etc. Take note of the wildcard ALL TABLES and ALL SEQUENCES options.

If this seems like too much hassle to do for each table, view, schema, sequence, etc, you can in Pg 9.1 and above use ALTER DEFAULT PRIVILEGES to change the default GRANTs on new objects.

Oracle – How to Generate Multiple Ranges Based on a Result Set

Solved this with help from https://stackoverflow.com/questions/3664903/how-can-i-return-multiple-identical-rows-based-on-a-quantity-field-in-the-row-it

The resulting answer with the original table looks like this:

with qtys as (
  select 3 as qty from dual union all
  select 10 as qty from dual union all
  select 9 as qty from dual union all
  select 7 as qty from dual union all
  select 9 as qty from dual union all
  select 3 as qty from dual
)
, results as (
  select n qty
  from qtys x
  join (
    select rownum n
    from dual
    connect by level <= (
      select max(qty)
      from qtys
    )
  ) y on y.n <= x.qty
)
select max(qty) qty
from (
  select count(1)
  , qty
  from results
  group by qty
  having count(1) = (
    select count(1)
    from qtys
  )
);

I'm certain I can condense it a little, but it produces the desired result.

EDIT

I suppose looking closer at this taking the minimum would have produced the same, desired result:

with qtys as (
  select 3 as qty from dual union all
  select 10 as qty from dual union all
  select 9 as qty from dual union all
  select 7 as qty from dual union all
  select 9 as qty from dual union all
  select 3 as qty from dual
)
select min(qty) qty
from qtys;

Best Answer

Related Solutions

Postgresql – Problem with permissions for user

Oracle – How to Generate Multiple Ranges Based on a Result Set

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