Alright so I have a table, in this table are two columns with ID's. I want to make one of the columns distinct, and once it is distinct to select all of those from the second column of a certain ID.
Originally I tried:
select distinct inp_kll_id from kb3_inv_plt where inp_plt_id = 581;
However this does the where clause first, and then returns distinct values.
Alternatively:
select * from (select distinct(inp_kll_id) from kb3_inv_plt) as inp_kll_id where inp_plt_id = 581;
However this cannot find the column inp_plt_id because distinct only returns the column, not the whole table.
Any suggestions?
Edit:
Each kll_id may have one or more plt_id. I would like unique kll_id's for a certain kb3_inv_plt id.
| inp_kll_id | inp_plt_id |
| 1941 | 41383 |
| 1942 | 41276 |
| 1942 | 38005 |
| 1942 | 39052 |
| 1942 | 40611 |
| 1943 | 5868 |
| 1943 | 4914 |
| 1943 | 39511 |
| 1944 | 39511 |
| 1944 | 41276 |
| 1944 | 40593 |
| 1944 | 26555 |
If you do mean, by "make distinct", "pick only inp_kll_ids that happen just once" (not the SQL semantics for Distinct), this should work:
select inp_kll_id
from kb3_inv_plt
group by inp_kll_id
having count(*)=1 and inp_plt_id = 581;
Get all the distinct first (alias 'a' in my following example) and then join it back to the table with the specified criteria (alias 'b' in my following example).
SELECT *
FROM (
SELECT
DISTINCT inp_kll_id
FROM kb3_inv_plt
) a
LEFT JOIN kb3_inv_plt b
ON a.inp_kll_id = b.inp_kll_id
WHERE b.inp_plt_id = 581
in this table are two columns with
ID's. I want to make one of the
columns distinct, and once it is
distinct to select all of those from
the second column of a certain ID.
SELECT distinct tableX.ID2
FROM tableX
WHERE tableX.ID1 = 581
I think your understanding of distinct may be different from how it works. This will indeed apply the where clause first, and then get a distinct list of unique entries of tableX.ID2, which is exactly what you ask for in the first part of your question.
By making a row distinct, you're ensuring no other rows are exactly the same. You aren't making a column distinct. Let's say your table has this data:
ID1 ID2
10 4
10 3
10 7
4 6
When you select distinct ID1,ID2 - you get the same as select * because the rows are already distinct.
Can you add information to clear up what you are trying to do?
Related
I have inherited a table where one column is a comma-separated list of primary keys for a different table:
id | other_ids | value
---|-----------|-------
1 | a,b,c | 100
2 | d,e | 200
3 | f,g | 3000
I would like to convert this table to one where each other_id gets a column of its own:
id | other_id
---|---------
1 | a
1 | b
1 | c
2 | d
2 | e
3 | f
3 | g
However, I cannot think of a way to do this?
The table is > 10 GB in size, so I would like to do this inside the database, if possible.
first time post, please be kind.
Try this
select id,SUBSTRING_INDEX(other_ids,',',1) as other_id from reverseconcat
UNION
select id,SUBSTRING_INDEX(SUBSTRING_INDEX(other_ids,',',2),',',-1) as other_id from reverseconcat
UNION
select id,SUBSTRING_INDEX(SUBSTRING_INDEX(other_ids,',',3),',',-1) as other_id from reverseconcat
order by id
Although I cant really take any credit. Found this on http://www.programering.com/a/MzMyUzNwATg.html
Unsure how you will go on a huge dataset. Also you will need to add more unions if the other_ids are > 3
If you have the other table, then you can use a join and find_in_set():
select t.id, ot.pk as other_id
from t join
othertable ot
on find_in_set(ot.pk, t.other_ids) > 0;
I have a table like this:
Table: p
+----------------+
| id | w_id |
+---------+------+
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 5 | 10 |
| 5 | 8 |
| 6 | 5 |
| 6 | 8 |
| 6 | 10 |
| 6 | 10 |
| 7 | 8 |
| 7 | 10 |
+----------------+
What is the best SQL to get the following result? :
+-----------------------------+
| id | most_used_w_id |
+---------+-------------------+
| 5 | 8 |
| 6 | 10 |
| 7 | 8 |
+-----------------------------+
In other words, to get, per id, the most frequent related w_id.
Note that on the example above, id 7 is related to 8 once and to 10 once.
So, either (7, 8) or (7, 10) will do as result. If it is not possible to
pick up one, then both (7, 8) and (7, 10) on result set will be ok.
I have come up with something like:
select counters2.p_id as id, counters2.w_id as most_used_w_id
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters2
join (
select p_id, max(count_of_w_ids) as max_counter_for_w_ids
from (
select p.id as p_id,
w_id,
count(w_id) as count_of_w_ids
from p
group by id, w_id
) as counters
group by p_id
) as p_max
on p_max.p_id = counters2.p_id
and p_max.max_counter_for_w_ids = counters2.count_of_w_ids
;
but I am not sure at all whether this is the best way to do it. And I had to repeat the same sub-query two times.
Any better solution?
Try to use User defined variables
select id,w_id
FROM
( select T.*,
if(#id<>id,1,0) as row,
#id:=id FROM
(
select id,W_id, Count(*) as cnt FROM p Group by ID,W_id
) as T,(SELECT #id:=0) as T1
ORDER BY id,cnt DESC
) as T2
WHERE Row=1
SQLFiddle demo
Formal SQL
In fact - your solution is correct in terms of normal SQL. Why? Because you have to stick with joining values from original data to grouped data. Thus, your query can not be simplified. MySQL allows to mix non-group columns and group function, but that's totally unreliable, so I will not recommend you to rely on that effect.
MySQL
Since you're using MySQL, you can use variables. I'm not a big fan of them, but for your case they may be used to simplify things:
SELECT
c.*,
IF(#id!=id, #i:=1, #i:=#i+1) AS num,
#id:=id AS gid
FROM
(SELECT id, w_id, COUNT(w_id) AS w_count
FROM t
GROUP BY id, w_id
ORDER BY id DESC, w_count DESC) AS c
CROSS JOIN (SELECT #i:=-1, #id:=-1) AS init
HAVING
num=1;
So for your data result will look like:
+------+------+---------+------+------+
| id | w_id | w_count | num | gid |
+------+------+---------+------+------+
| 7 | 8 | 1 | 1 | 7 |
| 6 | 10 | 2 | 1 | 6 |
| 5 | 8 | 3 | 1 | 5 |
+------+------+---------+------+------+
Thus, you've found your id and corresponding w_id. The idea is - to count rows and enumerate them, paying attention to the fact, that we're ordering them in subquery. So we need only first row (because it will represent data with highest count).
This may be replaced with single GROUP BY id - but, again, server is free to choose any row in that case (it will work because it will take first row, but documentation says nothing about that for common case).
One little nice thing about this is - you can select, for example, 2-nd by frequency or 3-rd, it's very flexible.
Performance
To increase performance, you can create index on (id, w_id) - obviously, it will be used for ordering and grouping records. But variables and HAVING, however, will produce line-by-line scan for set, derived by internal GROUP BY. It isn't such bad as it was with full scan of original data, but still it isn't good thing about doing this with variables. On the other hand, doing that with JOIN & subquery like in your query won't be much different, because of creating temporery table for subquery result set too.
But to be certain, you'll have to test. And keep in mind - you already have valid solution, which, by the way, isn't bound to DBMS-specific stuff and is good in terms of common SQL.
Try this query
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having max(ccc)
here is the sqlfidddle link
You can also use this code if you do not want to rely on the first record of non-grouping columns
select p_id, ccc , w_id from
(
select p.id as p_id,
w_id, count(w_id) ccc
from p
group by id,w_id order by id,ccc desc) xxx
group by p_id having ccc=max(ccc);
I have two tables
Table: color_document
+----------+---------------------+
| color_id | document_id |
+----------+---------------------+
| 180907 | 4270851 |
| 180954 | 4270851 |
+----------+---------------------+
Table: color_group
+----------------+-----------+
| color_group_id | color_id |
+----------------+-----------+
| 3 | 180954 |
| 4 | 180907 |
| 11 | 180907 |
| 11 | 180984 |
| 12 | 180907 |
| 12 | 180954 |
+----------------+-----------+
Is it possible for a query to get a result that looks something like this using multiple color id's to join the two tables?
Result
+----------------+--------------+
| color_group_id | document_id |
+----------------+--------------+
| 12 | 4270851 |
+----------------+--------------+
Since Color Group 12 is the only group that has the exact same set of Colors that Document 4270851 has.
I've got some bad data that i'm being forced to work with so I've had to manufacture the color groups by finding each unique set of color_id's associated with document_id's. I'm trying to then create a new relationship directly between my manufactured color groups and documents.
I know I could probably do something with a GROUP_CONCAT to make a pseudo key of concatenated color ids, but I'm trying to find a solution that would also work in, say, Oracle. Am I barking up the completely wrong tree with this logic?
My ultimate goal is to be able to have a single row in a table that would represent any number of Colors that are associated with a Document to be exported to a completely different system than the one I'm working with.
Any thoughts/comments/suggestions are greatly appreciated.
Thank you in advance for looking at my question.
Do a normal join of the two tables, and count the number of rows in each pairing. Then test whether this is the same as the number of times each of the items appears in the original tables. If all are the same, then all color IDs must match.
SELECT a.color_group_id, a.document_id
FROM (
SELECT color_group_id, document_id, COUNT(*) ct
FROM color_document d
JOIN color_group g ON d.color_id = g.color_id
GROUP BY color_group_id, document_id) a
JOIN (
SELECT color_group_id, COUNT(*) ct
FROM color_group
GROUP BY color_group_id) b
ON a.color_group_id = b.color_group_id and a.ct = b.ct
JOIN (
SELECT document_id, COUNT(*) ct
FROM color_document
GROUP BY document_id) c
ON a.document_id = c.document_id and a.ct = c.ct
SQLFIDDLE
If i understand your question correct you just have to join the two tables and then group the results by color_group_id an document_id.
SQL Fiddle
select color_group_id, document_id
from
color_document cd join
color_group cg
on cd.color_id = cg.color_id
group by color_group_id, document_id
That query will give you this result set:
COLOR_GROUP_ID DOCUMENT_ID
3 4270851
4 4270851
11 4270851
12 4270851
Is that what you want?
I've got a table with the most common colors in images. It looks something like this:
file | color | count
---------------------
1 | ffefad | 166
1 | 443834 | 84
2 | 74758a | 3874
2 | abcdef | 228
2 | 876543 | 498
3 | 543432 | 3382
3 | abcdef | 483
I'm trying to get the most common color for each image. So I'd like my result to be:
file | color | count
---------------------
1 | ffefad | 166
2 | 74758a | 3874
3 | 543432 | 3382
So my problem seems to be that I need to GROUP BY the file column, but MAX() the count column. But simply
SELECT h.file, h.color, MAX(h.count) FROM histogram GROUP BY h.file
isn't working because it's indeterminate, so the color result won't match the row from the count result.
SELECT h.file, h.color, MAX(h.count) FROM histogram GROUP BY h.file, h.color
fixes the determinacy, but now every row is "unique" and all rows are returned.
I can't figure out a way to do a subquery or join, since the only "correct" values I can figure to get, file and count, are not distinct by themselves.
Perhaps I need a saner schema? It's "my" table so I can change that if need be.
SELECT tbl.file, tbl.color, tbl.count
FROM tbl
LEFT JOIN tbl as lesser
ON lesser.file = tbl.file
AND tbl.count < lesser.count
WHERE lesser.file IS NULL
order by tbl.file
select file , max(count)
FROM histogram
GROUP BY h.file
This will give the max(count) by file. Turn it into a subquery and inner join so it acts as a filter.
select h.file, h.colour, h.count
from histogram inner join
(select file , max(count) as maxcount
FROM histogram
GROUP BY h.file) a
on a.file = h.file and a.maxcount = h.count
This will respond with 2 rows if there are more than 1 colour with the same max count.
For this problem, consider the following 3 tables:
Event
id (pk)
title
Event_Category
event_id (pk, fk)
category_id (pk, fk)
Category
id (pk)
description
Pretty trivial I guess... :) Each event can fall into zero or more categories, in total there are 4 categories.
In my application, I want to view and edit the categories for a specific event. Graphically, the event will be shown together with ALL categories and a checkbox indicating whether the event falls into the category. Changing and saving the choice will result in modifocation of the intermediate table Event_Category.
But first: how to select this for a specific event? The query I need will in fact always return 4 rows, the number of categories present.
Following returns only the entries for the categories the event with id=11 falls into. Experimenting with outer joins did not give more rows in the result.
SELECT e.id, c.omschrijving
FROM Event e
INNER JOIN Event_Categorie ec ON e.id = ec.event_id
INNER JOIN Categorie c ON c.id = ec.categorie_id
WHERE e.id = 11
Or should I start with the Category table in the query? Hope for some hints :)
TIA, Klaas
UPDATE:
Yes I did but still have not found the answer. But I have simplified the issue by omitting the Event table from the query because this table is only used to view the Event descriptions.
SELECT * from Categorie c LEFT JOIN Event_Categorie ec ON c.id = ec.categorie_id WHERE ec.event_id = 11;
The simplified 2-table query only uses the lookup table and the link table but still returns only 2 rows instead of the total of 4 rows in the Categorie table.
My guess would be that the WHERE clause is applied after the joining, so the rows not joined to the link table are excluded. In my application I solved the issues by using a subquery but I still would like to know what is the best solution.
What you want is the list of all categories, plus information about whether that category is in the list of categories of your event.
So, you can do:
SELECT
*
FROM
Category
LEFT JOIN Event_Category ON category_id = id
WHERE
event_id = 11
and event_id column will be NULL on the categories that are not part of your event.
You can also create a column (named has_category below) that you will use to see if the event has this category instead of comparing with NULL:
SELECT
*,
event_id IS NOT NULL AS has_category
FROM
Category
LEFT JOIN Event_Category ON category_id = id
WHERE
event_id = 11
EDIT: This seems exactly what you say you are doing on your edit. I tested it and it seems correct. Are you sure you are running this query, and that rows with NULL are not somehow ignored?
The query
SELECT * FROM Categorie;
returns 4 rows:
+----+--------------+-------------------------------------+--------------------------------------+
| id | omschrijving | afbeelding | afbeelding_klein |
+----+--------------+-------------------------------------+--------------------------------------+
| 1 | Creatief | images/categorieen/creatief420k.jpg | images/categorieen/creatief190k.jpg |
| 2 | Sportief | images/categorieen/sportief420k.jpg | images/categorieen/sportief190kr.jpg |
| 4 | Culinair | images/categorieen/culinair420k.jpg | images/categorieen/culinair190k.jpg |
| 5 | Spirit | images/categorieen/spirit420k.jpg | images/categorieen/spirit190k.jpg |
+----+--------------+-------------------------------------+--------------------------------------+
4 rows in set (0.00 sec)
BUT:
The query
SELECT *
FROM Categorie
LEFT JOIN Event_Categorie ON categorie_id = id
WHERE event_id = 11;
returns 2 rows:
+----+--------------+-------------------------------------+-------------------------------------+----------+--------------+
| id | omschrijving | afbeelding | afbeelding_klein | event_id | categorie_id |
+----+--------------+-------------------------------------+-------------------------------------+----------+--------------+
| 1 | Creatief | images/categorieen/creatief420k.jpg | images/categorieen/creatief190k.jpg | 11 | 1 |
| 4 | Culinair | images/categorieen/culinair420k.jpg | images/categorieen/culinair190k.jpg | 11 | 4 |
+----+--------------+-------------------------------------+-------------------------------------+----------+--------------+
2 rows in set (0.00 sec)
So I still need the subquery... and the LEFT JOIN is not effective in showing all rows of the CAtegorie table, regardless whether there is a match with the link table.
This query, however, does what I want it to do:
SELECT *
FROM Categorie c
LEFT JOIN (SELECT * FROM Event_Categorie ec WHERE ec.event_id = 11 ) AS subselect ON subselect.categorie_id = c.id;
Result:
+----+--------------+-------------------------------------+--------------------------------------+----------+--------------+
| id | omschrijving | afbeelding | afbeelding_klein | event_id | categorie_id |
+----+--------------+-------------------------------------+--------------------------------------+----------+--------------+
| 1 | Creatief | images/categorieen/creatief420k.jpg | images/categorieen/creatief190k.jpg | 11 | 1 |
| 2 | Sportief | images/categorieen/sportief420k.jpg | images/categorieen/sportief190kr.jpg | NULL | NULL |
| 4 | Culinair | images/categorieen/culinair420k.jpg | images/categorieen/culinair190k.jpg | 11 | 4 |
| 5 | Spirit | images/categorieen/spirit420k.jpg | images/categorieen/spirit190k.jpg | NULL | NULL |
+----+--------------+-------------------------------------+--------------------------------------+----------+--------------+
4 rows in set (0.00 sec)
The issue is that you have filtered the results by the eventid. As you can see in your results, two of the categories (Sportief and Spirit) do not have events. So the correct SQL statement (using SQL Server syntax; some translation may be required) is:
SELECT *
FROM Categorie
LEFT JOIN Event_Categorie ON categorie_id = id
WHERE (event_id IS NULL) OR (event_id = 11);
Finally I found the right query, no subselect is necessary. But the WHERE clause works after the joining and therefore is no part of the join anymore. THe solution is extending the ON clause with an extra condition. Now all 4 rows are returned with NULL for the non-matching Categories!
SELECT *
FROM Categorie
LEFT JOIN Event_Categorie ON categorie_id = id AND event_id = 11;
So the bottom line is that putting an extra condition in the ON clause has different effect than filtering out rows by the same condition in the WHERE clause!