I have the following working sql sequence:
SELECT *, films.category AS filmCategory
FROM ( SELECT *
FROM films
ORDER BY `unique` ASC
LIMIT 6, 4) films
LEFT OUTER JOIN items ON items.unique = films.ref
ORDER BY films.unique ASC
This works well and selects the correct four elements from the DB. However, I have some rules that I check for using WHERE, that I can't get working. I have done the following:
SELECT *, films.category AS filmCategory
FROM ( SELECT *
FROM films
ORDER BY `unique` ASC
LIMIT 6, 4) films
LEFT OUTER JOIN items ON items.unique = films.ref
WHERE films.youtube IS NOT NULL AND films.youtube <> ''
ORDER BY films.unique ASC
where the only difference is the added line with the WHERE clause. But this doesn't work - in fact it makes no difference from before but returns the same rows.
How can I include these WHERE rules correctly in this sql sentence?
Note
The line films.youtube IS NOT NULL AND films.youtube <> '' is checking if a specific cell is empty. This is made with help from this question
Perhaps you are looking for a where clause in the subquery? That way, the limit will be applied after your where clause.
SELECT *, films.category AS filmCategory
FROM ( SELECT *
FROM films
WHERE films.youtube IS NOT NULL AND films.youtube <> ''
ORDER BY `unique` ASC
LIMIT 6, 4) films
LEFT OUTER JOIN items ON items.unique = films.ref
ORDER BY films.unique ASC
A small additional suggestion. You can simplify:
WHERE films.youtube IS NOT NULL AND films.youtube <> ''
to
WHERE films.youtube > ''
because null > '' is not true (but unknown.) Or perhaps more readable:
WHERE length(films.youtube) > 0
Related
I am trying to use COUNT(DISTINC column) OVER(PARTITION BY column) when I am using COUNT + window function(OVER).
I get an error like the one in the title and can't get it to work.
I have looked into how to deal with this error, but I have not found an example of how to deal with such a complex query as the one below.
I cannot find an example of how to deal with such a complex query as shown below, and I am not sure how to handle it.
The COUNT part of the problem exists on line 65.
How can such a complex query be resolved without slowing down?
WITH RECURSIVE "cte" AS((
SELECT
"videos_productvideocomment"."id",
"videos_productvideocomment"."user_id",
"videos_productvideocomment"."video_id",
"videos_productvideocomment"."parent_id",
"videos_productvideocomment"."text",
"videos_productvideocomment"."commented_at",
"videos_productvideocomment"."edited_at",
"videos_productvideocomment"."created_at",
"videos_productvideocomment"."updated_at",
"videos_productvideocomment"."id" AS "root_id"
FROM
"videos_productvideocomment"
WHERE
(
"videos_productvideocomment"."parent_id" IS NULL
AND "videos_productvideocomment"."video_id" = 'f264433c-c0af-49cc-8b40-84453da71b2d'
)
) UNION(
SELECT
"videos_productvideocomment"."id",
"videos_productvideocomment"."user_id",
"videos_productvideocomment"."video_id",
"videos_productvideocomment"."parent_id",
"videos_productvideocomment"."text",
"videos_productvideocomment"."commented_at",
"videos_productvideocomment"."edited_at",
"videos_productvideocomment"."created_at",
"videos_productvideocomment"."updated_at",
"cte"."root_id" AS "root_id"
FROM
"videos_productvideocomment"
INNER JOIN
"cte"
ON "videos_productvideocomment"."parent_id" = "cte"."id"
))
SELECT
*,
EXISTS(
SELECT
(1) AS "a"
FROM
"videos_productvideolikecomment" U0
WHERE
(
U0."comment_id" = t."id"
AND U0."user_id" = '3bd3bc86-0335-481e-9fd2-eb2fb1168f48'
)
LIMIT 1
) AS "liked"
FROM
(
SELECT DISTINCT
"cte"."id",
"cte"."created_at",
"cte"."updated_at",
"cte"."user_id",
"cte"."text",
"cte"."commented_at",
"cte"."edited_at",
"cte"."parent_id",
"cte"."video_id",
"cte"."root_id" AS "root_id",
COUNT(DISTINCT "cte"."root_id") OVER(PARTITION BY "cte"."root_id") AS "reply_count", <--- here
COUNT("videos_productvideolikecomment"."id") OVER(PARTITION BY "cte"."id") AS "liked_count"
FROM
"cte"
LEFT OUTER JOIN
"videos_productvideolikecomment"
ON (
"cte"."id" = "videos_productvideolikecomment"."comment_id"
)
) t
WHERE
t."id" = t."root_id"
ORDER BY
CASE
WHEN t."user_id" = '3bd3bc86-0335-481e-9fd2-eb2fb1168f48' THEN 0
ELSE 1
END ASC,
"liked_count" DESC
DISTINCT will look for duplicates and remove it, but in big data it will take a lot of time to process this query, you should process the middle of the record in the programming part I think it will be fast than. Thank
Can someone please tell me why the COALESCE is working on the first SELECT here and not the other two? I'm still getting NULL values on the second two statements.
(SELECT COALESCE(DEFax, NULL, '') FROM Debtor d WHERE d.DEIsPrimary = 1 AND d.CApKey = c.CApKey) AS FaxNumberOne,
(SELECT COALESCE(DEFax, NULL, '') FROM (SELECT ROW_NUMBER() OVER (ORDER BY DEpKey ASC)
AS rownumber, DEFax FROM Debtor d WHERE d.CApKey = c.CApKey AND d.DEIsPrimary <> 1)
AS foo WHERE rownumber = 1) AS FaxNumberTwo,
(SELECT COALESCE(DEFax, NULL, '') FROM (SELECT ROW_NUMBER() OVER (ORDER BY DEpKey ASC)
AS rownumber, DEFax FROM Debtor d WHERE d.CApKey = c.CApKey AND d.DEIsPrimary <> 1)
AS foo WHERE rownumber = 2) AS FaxNumberThree
Thanks!
Sample data and desired results would really help.
But a scalar subquery is a subquery that returns one column and zero or one rows. If it returns zero rows, then the value is NULL regardless of the expression in the SELECT. In other words, the COALESCE() needs to go outside, something like this:
coalesce( (select . . . . ),
''
)
Including NULL in the coalesce() list is not a good practice. It is unnecessary and misleading -- and always ignored.
I'm creating a view in MariaDB and i'm having trouble making it work for a couple of fields. Currently this is working:
( SELECT DISTINCT IFNULL(grades.`grade`,'No Grade')
FROM `table` grades
WHERE userinfo.`id` = grades.`id`
AND grades.`Item Name` = 'SOMEINFO'
) 'SOMENAME',
But i need to add a select where the 'No grade' is, in the following form
( SELECT DISTINCT IFNULL( grades.`grade`,
SELECT IF( EXISTS
( SELECT *
FROM `another_table`
WHERE userid = 365
AND courseid = 2
), 'Enrolled', 'Not enrolled'
)
)
FROM `table` grades
WHERE userinfo.`id` = grades.`id`
AND grades.`Item Name` = 'SOMEINFO'
) 'SOMENAME',
i know that
SELECT IF( EXISTS( SELECT *
FROM `another_table`
WHERE userid = 365
AND courseid = 2
),
'Enrolled', 'Not enrolled'
)
is working too, but now the whole thing it's giving me an error, so any suggestions would be greatly appreciated
Thanks
This looks like a subquery:
(SELECT DISTINCT IFNULL(grades.`grade`,
SELECT IF( EXISTS (SELECT *
FROM `another_table`
WHERE userid = 365 AND courseid = 2
), 'Enrolled', 'Not enrolled'
)
)
FROM `table` grades
WHERE userinfo.`id` = grades.`id` AND
grades.`Item Name` = 'SOMEINFO'
) as SOMENAME,
You are using a subquery that returns two columns in a position where a scalar subquery is expected. A scalar subquery returns one column in at most one row.
Unfortunately, there is no easy way to do what you want in MySQL, because of the restrictions on views. I would advise you to rewrite the logic so the exists is handled using a left join in the from clause.
The query below accesses the Votes table that contains over 30 million rows. The result set is then selected from using WHERE n = 1. In the query plan, the SORT operation in the ROW_NUMBER() windowed function is 95% of the query's cost and it is taking over 6 minutes to complete execution.
I already have an index on same_voter, eid, country include vid, nid, sid, vote, time_stamp, new to cover the where clause.
Is the most efficient way to correct this to add an index on vid, nid, sid, new DESC, time_stamp DESC or is there an alternative to using the ROW_NUMBER() function for this to achieve the same results in a more efficient manner?
SELECT v.vid, v.nid, v.sid, v.vote, v.time_stamp, v.new, v.eid,
ROW_NUMBER() OVER (
PARTITION BY v.vid, v.nid, v.sid ORDER BY v.new DESC, v.time_stamp DESC) AS n
FROM dbo.Votes v
WHERE v.same_voter <> 1
AND v.eid <= #EId
AND v.eid > (#EId - 5)
AND v.country = #Country
One possible alternative to using ROW_NUMBER():
SELECT
V.vid,
V.nid,
V.sid,
V.vote,
V.time_stamp,
V.new,
V.eid
FROM
dbo.Votes V
LEFT OUTER JOIN dbo.Votes V2 ON
V2.vid = V.vid AND
V2.nid = V.nid AND
V2.sid = V.sid AND
V2.same_voter <> 1 AND
V2.eid <= #EId AND
V2.eid > (#EId - 5) AND
V2.country = #Country AND
(V2.new > V.new OR (V2.new = V.new AND V2.time_stamp > V.time_stamp))
WHERE
V.same_voter <> 1 AND
V.eid <= #EId AND
V.eid > (#EId - 5) AND
V.country = #Country AND
V2.vid IS NULL
The query basically says to get all rows matching your criteria, then join to any other rows that match the same criteria, but which would be ranked higher for the partition based on the new and time_stamp columns. If none are found then this must be the row that you want (it's ranked highest) and if none are found that means that V2.vid will be NULL. I'm assuming that vid otherwise can never be NULL. If it's a NULLable column in your table then you'll need to adjust that last line of the query.
I use complex CASE WHEN for selecting values. I would like to use this result in WHERE clause, but Postgres says column 'd' does not exists.
SELECT id, name, case when complex_with_subqueries_and_multiple_when END AS d
FROM table t WHERE d IS NOT NULL
LIMIT 100, OFFSET 100;
Then I thought I can use it like this:
select * from (
SELECT id, name, case when complex_with_subqueries_and_multiple_when END AS d
FROM table t
LIMIT 100, OFFSET 100) t
WHERE d IS NOT NULL;
But now I am not getting a 100 rows as result. Probably (I am not sure) I could use LIMIT and OFFSET outside select case statement (where WHERE statement is), but I think (I am not sure why) this would be a performance hit.
Case returns array or null. What is the best/fastest way to exclude some rows if result of case statement is null? I need 100 rows (or less if not exists - of course). I am using Postgres 9.4.
Edited:
SELECT count(*) OVER() AS count, t.id, t.size, t.price, t.location, t.user_id, p.city, t.price_type, ht.value as houses_type_value, ST_X(t.coordinates) as x, ST_Y(t.coordinates) AS y,
CASE WHEN t.classification='public' THEN
ARRAY[(SELECT i.filename FROM table_images i WHERE i.table_id=t.id ORDER BY i.weight ASC LIMIT 1), t.description]
WHEN t.classification='protected' THEN
ARRAY[(SELECT i.filename FROM table_images i WHERE i.table_id=t.id ORDER BY i.weight ASC LIMIT 1), t.description]
WHEN t.id IN (SELECT rl.table_id FROM table_private_list rl WHERE rl.owner_id=t.user_id AND rl.user_id=41026) THEN
ARRAY[(SELECT i.filename FROM table_images i WHERE i.table_id=t.id ORDER BY i.weight ASC LIMIT 1), t.description]
ELSE null
END AS main_image_description
FROM table t LEFT JOIN table_modes m ON m.id = t.mode_id
LEFT JOIN table_types y ON y.id = t.type_id
LEFT JOIN post_codes p ON p.id = t.post_code_id
LEFT JOIN table_houses_types ht on ht.id = t.houses_type_id
WHERE datetime_sold IS NULL AND datetime_deleted IS NULL AND t.published=true AND coordinates IS NOT NULL AND coordinates && ST_MakeEnvelope(17.831490030182, 44.404640972306, 12.151558389557, 47.837396630872) AND main_image_description IS NOT NULL
GROUP BY t.id, m.value, y.value, p.city, ht.value ORDER BY t.id LIMIT 100 OFFSET 0
To use the CASE WHEN result in the WHERE clause you need to wrap it up in a subquery like you did, or in a view.
SELECT * FROM (
SELECT id, name, CASE
WHEN name = 'foo' THEN true
WHEN name = 'bar' THEN false
ELSE NULL
END AS c
FROM case_in_where
) t WHERE c IS NOT NULL
With a table containing 1, 'foo', 2, 'bar', 3, 'baz' this will return records 1 & 2. I don't know how long this SQL Fiddle will persist, but here is an example: http://sqlfiddle.com/#!15/1d3b4/3 . Also see https://stackoverflow.com/a/7950920/101151
Your limit is returning less than 100 rows if those 100 rows starting at offset 100 contain records for which d evaluates to NULL. I don't know how to limit the subselect without including your limiting logic (your case statements) re-written to work inside the where clause.
WHERE ... AND (
t.classification='public' OR t.classification='protected'
OR t.id IN (SELECT rl.table_id ... rl.user_id=41026))
The way you write it will be different and it may be annoying to keep the CASE logic in sync with the WHERE limiting statements, but it would allow your limits to work only on matching data.