sql SERVER - distinct selection based on priority columns - sql

Question

hello I would like to find a solution to solve my problem in a single request if possible.
For the moment I take all the records then I go through the lines one by one to eliminate what I don't want.
I have 2 tables : first table with links
the second with the prefered label for the url
the second table must be consulted keeping only the row with maximum priority
priority rules are
the current user then
the user group and finally
everyone.
if the hidden column is true, exclude any reference to the url
here is the expected result.
Unfortunately, I don't see any other solution than to multiply the conditions on several selects and unions.
if you have a idea to solve my problem, thank you in advance for your help

Answer 1

It appears as though you can rely on pref_id for the preference ordering, correct? If so, you could try:
SELECT *
FROM table2
INNER JOIN table1 ON table2.url_id = table1.url_id
QUALIFY ROW_NUMBER() OVER (
PARTITION BY table1.url
ORDER BY pref_id ASC
) = 1
This will partition by the url and then provide only the one with lowest pref_id.
I didn't test this SQL as I wasn't sure which RDBMS you're running on, but I used Rasgo to translate the SQL.

Answer 2

maybe of interest in this tricky query:
select so.*, table1.url from
(select distinct t.url_id,
(select pref_id from table2 s where s.url_id = t.url_id order by "user" is null, "group" is null limit 1) pref_id
from table2 t
where not exists(select 1 from table2 s where s.hide and s.url_id = t.url_id)
) ids
join table2 so on so.pref_id = ids.pref_id
join table1 ON table1.url_id = ids.url_id
order by so.url_id;

Answer 3

here is my solution but i think there is better to do.
in the condition's select, I built a column which gives a level note according to the priorities
DECLARE #CUR_USER VARCHAR(10) = 'ROBERT'
DECLARE #CUR_GROUP VARCHAR(10) = 'DEV'
DECLARE #TABLE1 TABLE (
URL_ID INT
,URLNAME VARCHAR(100)
);
DECLARE #TABLE2 TABLE (
PREF_ID INT
,URL_ID INT
,FAVORITE_LABEL VARCHAR(100)
,USER_GROUP VARCHAR(10)
,USER_CODE VARCHAR(10)
,HIDE_URL DECIMAL(1, 0) DEFAULT 0
);
INSERT INTO #TABLE1
VALUES
(1, 'https://stackoverflow.com/')
,(2, 'https://www.microsoft.com/')
,(3, 'https://www.apple.com/')
,(4, 'https://www.wikipedia.org/')
;
INSERT INTO #TABLE2
VALUES
(1000, 1, 'find everything', NULL, 'ROBERT', 0)
,(1001, 1, 'a question ? find the answer here', 'DEV', NULL, 0)
,(1002, 1, 'StackOverFlow', NULL, NULL, 0)
,(1003, 2, 'Windows', 'DEV', NULL, 0)
,(1004, 2, 'Microsoft', NULL, NULL, 0)
,(1005, 3, 'Apple', NULL, NULL, 0)
,(1006, 4, 'Free encyclopedia', NULL, 'ROBERT', 1)
,(1007, 4, 'Wikipedia', NULL, NULL, 0)
,(1008, 1, 'StackOverFlow FOR MAT', 'MAT', NULL, 0)
,(1009, 2, 'Microsoft FOR MAT', 'MAT', NULL, 0)
,(1010, 3, 'Apple', 'MAT', NULL, 1)
,(1011, 4, 'Wikipedia FOR MAT', 'MAT', NULL, 0)
,(1012, 1, 'StackOverFlow', NULL, 'JEAN', 1)
,(1013, 2, 'Microsoft ', NULL, 'JEAN', 0)
,(1014, 3, 'Apple', NULL, 'JEAN', 0)
,(1015, 4, 'great encyclopedia', NULL, 'JEAN', 0)
;
SELECT t2.* ,t1.URLName
FROM #TABLE1 t1
INNER JOIN #TABLE2 t2 ON t1.URL_ID = t2.URL_ID
WHERE EXISTS (
SELECT 1
FROM (
SELECT TOP (1) test.PREF_ID
,CASE
-- if I do not comment this case: jean from the MAT group will not see apple
-- WHEN Hide_Url = 1
-- THEN 3
WHEN USER_code IS NOT NULL
THEN 2
WHEN USER_GROUP IS NOT NULL
THEN 1
ELSE 0
END AS ROW_LEVEL
FROM #TABLE2 test
WHERE (
(
test.USER_GROUP IS NULL
AND test.user_group IS NULL
AND test.USER_code IS NULL
)
OR (test.USER_GROUP = #CUR_GROUP)
OR (test.USER_code = #CUR_USER)
)
AND t2.URL_ID = test.URL_ID
ORDER BY ROW_LEVEL DESC
) test
WHERE test.PREF_ID = t2.PREF_ID
AND Hide_Url = 0
)

Answer 4

Simply use an ORDER BY clause that puts the preferred row first. You can use this in the window function ROW_NUMBER and work with this or use a lateral top(1) join with CROSS APPLY.
select *
from urls
cross apply
(
select top(1) *
from labels
where labels.url_id = urls.url_id
where [Group] is not null or [user] is not null or hide is not null
order by
case when [Group] is null then 2 else 1 end,
case when [user] is null then 2 else 1 end,
case when hide is null then 2 else 1 end
) top_labels
order by urls.url_id;