Can someone help me understand why the following query is not offsetting correctly?
It's meant to select all records in the games table, and add a column with a value of 0 or 1 based on whether a record in another table (wishlist) exists with the same gameId #memberId (in plain English, get me all records from games, and mark any game that exists in the wishlists table, under whatever memberId I give you)
SELECT *,
CASE WHEN wishlists.memberid IS NULL THEN 0 ELSE 1 END AS InMembersList
FROM games
INNER JOIN platforms ON games.platformid = platforms.id
LEFT OUTER JOIN wishlists ON games.id = wishlists.gameid and wishlists.memberid = #memberId
WHERE platforms.platformUrlId = #platformUrlId
ORDER BY releaseDate DESC
LIMIT 1,8
When I change the offset from 1 to 2, or 3, or whatever, many of the same records appear, which does not make any sense. Where am I going wrong?
Schema:
platforms(id, platform)
members(id, name)
games(id, platformId, releaseDate)
wishlists(id, memberId, gameId)
LIMIT 1,8 means start from row number 1 (they start from 0) and fetch 8 rows. So LIMIT 2,8 will give you 8 rows starting from row 2 - seven of which will be the same as with LIMIT 1,8
Related
Sorry if the title is misleading, I don't really know the terminology for what I want to accomplish. But let's consider this table:
CREATE TABLE entries (
id INT NOT NULL,
number INT NOT NULL
);
Let's say it contains four numbers associated with each id, like this:
id number
1 0
1 9
1 17
1 11
2 5
2 8
2 9
2 0
.
.
.
Is it possible, with a SQL-query only, to count the numbers of matches for any two given numbers (tuples) associated with a id?
Let's say I want to count the number of occurrences of number 0 and 9 that is associated with a unique id. In the sample data above 0 and 9 does occur two times (one time where id=1 and one time where id=2). I can't think of how to write a SQL-query that solves this. Is it possible? Maybe my table structure is wrong, but that's how my data is organized right now.
I have tried sub-queries, unions, joins and everything else, but haven't found a way yet.
You can use GROUP BY and HAVING clauses:
SELECT COUNT(s.id)
FROM(
SELECT t.id
FROM YourTable t
WHERE t.number in(0,9)
GROUP BY t.id
HAVING COUNT(distinct t.number) = 2) s
Or with EXISTS():
SELECT COUNT(distinct t.id)
FROM YourTable t
WHERE EXISTS(SELECT 1 FROM YourTable s
WHERE t.id = s.id and s.id IN(0,9)
HAVING COUNT(distinct s.number) = 2)
Im using MySQL
I cant change the DB structure, so thats not an option sadly
THE ISSUE:
When i use GROUP BY with CASE (as need in my situation), MYSQL uses
file_sort and the delay is humongous (approx 2-3minutes):
http://sqlfiddle.com/#!9/f97d8/11/0
But when i dont use CASE just GROUP BY group_id , MYSQL easily uses
index and result is fast:
http://sqlfiddle.com/#!9/f97d8/12/0
Scenerio: DETAILED
Table msgs, containing records of sent messages, with fields:
id,
user_id, (the guy who sent the message)
type, (0=> means it's group msg. All the msgs sent under this are marked by group_id. So lets say group_id = 5 sent 5 msgs, the table will have 5 records with group_id =5 and type=0. For type>0, the group_id will be NULL, coz all other types have no group_id as they are individual msgs sent to single recipient)
group_id (if type=0, will contain group_id, else NULL)
Table contains approx 10 million records for user id 50001 and with different types (i.e group as well as individual msgs)
Now the QUERY:
SELECT
msgs.*
FROM
msgs
INNER JOIN accounts
ON (
msgs.user_id = accounts.id
)
WHERE 1
AND msgs.user_id IN (50111)
AND msgs.type IN (0, 1, 5, 7)
GROUP BY CASE `msgs`.`type` WHEN 0 THEN `msgs`.`group_id` ELSE `msgs`.`id` END
ORDER BY `msgs`.`group_id` DESC
LIMIT 100
I HAVE to get summary in a single QUERY,
so msgs sent to group lets say 5 (have 5 records in this table) will be shown as 1 record for summary (i may show COUNT later, but thats not an issue).
The individual msgs have NULL as group_id, so i cant just put 'GROUP BY group_id ' coz that will Group all individual msgs to single record which is not acceptable.
Sample output can be something like:
id owner_id, type group_id COUNT
1 50001 0 2 5
1 50001 1 NULL 1
1 50001 4 NULL 1
1 50001 0 7 5
1 50001 5 NULL 1
1 50001 5 NULL 1
1 50001 5 NULL 1
1 50001 0 10 5
Now the problem is that the GROUP condition after using CASE (which i currently think that i have to because i only need to group by group_id if type=0) is causing alot of delay coz it's not using indexes which it does if i dont use CASE (like just group by group_id ). Please view SQLFiddles above to see the explain results
Can anyone plz give an advice how to get it optimized
UPDATE
I tried a workaround , that does somehow works out (drops INITIAL queries to 1sec). Using union, what it does is, to minimize the resultset by union that forces SQL to write on disk for filesort (due to huge resultset), limit the resultset of group msgs, and individual msgs (view query below)
-- first part of union retrieves group msgs (that have type 0 and needs to be grouped by group_id). Applies the limit to captivate the out of control result set
-- The second query retrieves individual msgs, (those with type !=0, grouped by msgs.id - not necessary but just to be save from duplicate entries due to joins). Applies the limit to captivate the out of control result set
-- JOins the two to retrieve the desired resultset
Here's the query:
SELECT
*
FROM
(
(
SELECT
msgs.id as reference_id, user_id, type, group_id
FROM
msgs
INNER JOIN accounts
ON (msgs.user_id = accounts.id)
WHERE 1
AND accounts.id IN (50111 ) AND type = 0
GROUP BY msgs.group_id
ORDER BY msgs.id DESC
LIMIT 40
)
UNION
ALL
(
SELECT
msgs.id as reference_id, user_id, type, group_id
FROM
msgs
INNER JOIN accounts
ON (
msgs.user_id = accounts.id
)
WHERE 1
AND msgs.type != 0
AND accounts.id IN (50111)
GROUP BY msgs.id
ORDER BY msgs.id
LIMIT 40
)
) AS temp
ORDER BY reference_id
LIMIT 20,20
But has alot of caveats,
-I need to handle the limit in inner queries as well. Lets say 20recs per page, and im on page 4. For inner queries , i need to apply limit 0,80, since im not sure which of the two parts had how many records in the previous 3 pages. So, as the records per page and number of pages grow, my query grows heavier. Lets say 1k rec per page, and im on page 100 , or 1K, the load gets heavier and time exponentially increases
I need to handle ordering in inner queries and then apply on the resultset prepared by union , conditions need to be applied on both inner queries seperately(but not much of an issue)
-Cant use calc_found_rows, so will need to get count using queries seperately
The main issue is the first one. The higher i go with the pagination , the heavier it gets
Would this run faster?
SELECT id, user_id, type, group_id
FROM
( SELECT id, user_id, type, group_id, IFNULL(group_id, id) AS foo
FROM msgs
WHERE user_id IN (50111)
AND type IN (0, 1, 5, 7)
)
GROUP BY foo
ORDER BY `group_id` DESC
LIMIT 100
It needs INDEX(user_id, type).
Does this give the 'correct' answer?
SELECT DISTINCT *
FROM msgs
WHERE user_id IN (50111)
AND type IN (0, 1, 5, 7)
GROUP BY IFNULL(group_id, id)
ORDER BY `group_id` DESC
LIMIT 100
(It needs the same index)
Table
id user_id rank_solo lp
1 1 15 45
2 2 7 79
3 3 17 15
How can I sort out a ranking query that sorts on rank_solo ( This ranges from 0 to 28) and if rank_solo = rank_solo , uses lp ( 0-100) to further determine ranking?
(If lp = lp, add a ranking for no tie rankings)
The query should give me the ranking from a certain random user_id. How is this performance wise on 5m+ rows?
So
User_id 1 would have ranking 2
User_id 2 would have ranking 3
User_id 3 would have ranking 1
You can get the ranking using variablesL
select t.*, (#rn := #rn + 1) as ranking
from t cross join
(select #rn := 0) params
order by rank_solo desc, lp;
You can use ORDER BY to sort your query:
SELECT *
FROM `Table`
ORDER BY rank_solo, lp
I'm not sure I quite understand what you're saying. With that many rows, create a query on the fields you're using to do your selects. For example, in MySQL client use:
create index RANKINGS on mytablename(rank_solo,lp,user_id);
Depending on what you use in your query to select the data, you may change the index or add another index with a different field combination. This has improved performance on my tables by a factor of 10 or more.
As for the query, if you're selecting a specific user then could you not just use:
select rank_solo from table where user_id={user id}
If you want the highest ranking individual, you could:
select * from yourtable order by rank_solo,lp limit 1
Remove the limit 1 to list them all.
If I've misunderstood, please comment.
An alternative would be to use a 2nd table.
table2 would have the following fields:
rank (auto_increment)
user_id
rank_solo
lp
With the rank field as auto increment, as it's populated, it will automatically populate with values beginning with "1".
Once the 2nd table is ready, just do this when you want to update the rankings:
delete from table2;
insert into table2 select user_id,rank_solo,lp from table1 order by rank_solo,lp;
It may not be "elegant" but it gets the job done. Plus, if you create an index on both tables, this query would be very quick since the fields are numeric.
I have a query which actually have a sorting using order by clause. i have a table like following...
user_id user_name user_age user_state user_points
1 Rakul 30 CA 56
2 Naydee 29 NY 144
3 Jeet 40 NJ 43
.....
i have following query...
select * from users where user_state = 'NY' order by user_points desc limit 50;
This gives me the list of 50 people with most points. I wanted to give least preference to few people who's id's were known. Incase if i do not have enough 50 records then those id's should come in the last in the list. I do not want the users 2 and 3 to come on top of the list even though they have higher points... those people should come on the last of the list from the query. Is there any way to push specific records to last on result set irrespective of query sorting ?
If you want to move specific records (like user_id = 2 and 3) down to the list; Then you can run below Query:
mysql> select *,IF(user_id=2 or user_id=3,0,1) as list_order from users where user_state = 'NY' order by list_order desc, user_points desc limit 50;
select * from (
select *
from users
where user_state = 'NY'
-- this order by ensures that 2 and 3 are included
order by case when user_id in (2,3) then 1 else 2 end, user_points desc
limit 50
) as top48plus2n3
-- this order by ensures that 2 and 3 are last
order by case when user_id in (2,3) then 2 else 1 end, user_points desc
Edit: changed id by user_id and corrected outside order by (sorry about that)
On the inner select:
By using this case calculation, what you do is ensuring that records with ids equal to 2 and 3 are "important" (firstly ordered in the order by). Those receive 1 while the others receive 2 as order value, only after that points are relevant.
On the outer select:
Records with ids 2 and 3 recieve 2 as order value, while the rest recieve 1. So they go last irrespective of its "default"
Here you have a reduced fiddle http://sqlfiddle.com/#!9/377c1/1
I'm trying to select the top 3 entries from a table called games that has foreign keys to the players and 2 ints for individual scores for the host and opponent.
The Query:
SELECT
games.id, games.host_score, games.opponent_score, player.name
FROM games, player
WHERE player.id = games.host_player_id
|| player.id = games.opponent_player_id
ORDER BY games.host_score, games.opponent_score DESC LIMIT 3
The query completes but it comes back out of order:
id host_score opponent_score name
17 0 0 Temp2
17 0 0 Temp0
16 770 930 Temp0
When I run a query that doesn't have an OR it works. How can I get this method working?
Also is there a way to set a LIMIT of 50 but not count duplicates?
For example if i wanted a limit of 2 but 3 people have the score 50 and 2 people have the score 20 it would return :
id host_score opponent_score name
17 50 0 Temp2
17 50 0 Temp0
17 50 0 Temp1
17 20 0 Temp3
17 20 0 Temp4
Or would it be better to run it as seperate quesies in php?
If you want to order from highest to lowest, you need to specify it for each field
ORDER BY games.host_score DESC, games.opponent_score DESC
Because when you don't specify the order it assumes you want the ascending order
I think your query is wrong, because one game will be on two rows -- one for the host and one for the opponent.
You want to get both the host and opponent names, so you need to join twice to the player table:
SELECT g.id, g.host_score, g.opponent_score, hp.name as HostName, op.name as OpponentName
FROM games g join
player hp
on hp.id = g.host_player_id join
player op
on op.id = g.opponent_player_id
ORDER BY g.host_score, g.opponent_score DESC
LIMIT 3
You should use OR (instead of ||) in SQL, also add parenthesis to make it readable.
WHERE (player.id = games.host_player_id) OR (player.id = games.opponent_player_id)
To get top 50 scores by the score values, though the total row count returned may be higher.
Use the barebones query below and tweak it to your needs.
SELECT g1.id, g1.host_scores, COUNT(g2.host_scores) AS Rank
FROM games g1
WHERE Rank <= 50
JOIN games g2 ON (g1.host_scores < g2.host_scores) OR (g1.host_scores=g2.host_scores)
GROUP BY g1.id, g1.host_scores
ORDER BY g1.host_scores DESC;
I must add that for such things to avoid complexity you can also get the data to your
application and easily do this in a programming language like Java, PHP etc.
It may result in you making more than one query but is far more simpler and more
maintainable over time.