So I have a query like
SELECT * FROM table WHERE id IN (1,2,3) LIMIT 10
Is it possible to limit the number of output for each of element in array like
SELECT * FROM table WHERE id 1 LIMIT 10
SELECT * FROM table WHERE id 2 LIMIT 10
SELECT * FROM table WHERE id 3 LIMIT 10
Yes, you can do it using variables:
SELECT *
FROM (
SELECT *,
#seq := IF(id = #id, #seq + 1,
IF(#id := id, 1, 1)) AS seq
FROM table
CROSS JOIN (SELECT #seq := 0, #id := 0) AS vars
WHERE id IN (1,2,3)
ORDER BY id) AS t
WHERE t.seq <= 10
If you're scared of MySQL variables (I am), you could also use a UNION query:
(SELECT * FROM table WHERE id = 1 LIMIT 10)
UNION ALL
(SELECT * FROM table WHERE id = 2 LIMIT 10)
UNION ALL
(SELECT * FROM table WHERE id = 3 LIMIT 10)
Related
Need assistance with simplifying this SQL query to possibly a single SELECT:
(SELECT * FROM `deals`
WHERE category_id = 1
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 2
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 4
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 5
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 6
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 8
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 9
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 10
ORDER BY id desc
LIMIT 10)
UNION
(SELECT * FROM `deals`
WHERE category_id = 17
ORDER BY id desc
LIMIT 10)
I've been told to try using GROUP BY and HAVING. However, any query I tried didn't work in the slightest...
Any help will be greatly appreciated!
EDIT - apologies, forgot to mention database engine is MySQL
You can condense this down with a window function to limit each group bucket to 10.
SELECT
*
FROM
(
SELECT
*,
ROW_NUMBER() OVER PARTITION BY(category_id ORDER BY id DESC) AS GroupOrder
FROM `deals`
WHERE category_id BETWEEN 1 AND 10
)AS X
WHERE
GroupOrder<=10
I'm not sure, I need to know if you need that limit of 10, is this like take top 10 of all those things?
if not then
SELECT * FROM `deals`
WHERE category_id between 0 and 10 or category_id=17
ORDER BY category_id asc, id desc
For older versions of MySQL without the windowing functions, here is the code.
SELECT T1.ID, T1.Category_ID, T1.Name
FROM (
SELECT #row_num := IF(#prev_value=concat_ws('',t.Category_ID),#row_num+1,1) AS RowNumber
,t.*
,#prev_value := concat_ws('',t.Category_ID)
FROM data t,
(SELECT #row_num := 1) x,
(SELECT #prev_value := '') y
ORDER BY t.Category_ID
) T1
WHERE T1.RowNumber < 10
AND T1.Category_ID IN (1,2,3,4,5,6,7,8,9,10)
You will need to add the necessary field names to the other select.
This uses the technique described here
I have a below table and wants to select only last 2 entries of all users.
Source table:
-------------------------------------
UserId | QuizId(AID)|quizendtime(AID)|
--------------------------------------
1 10 2016-5-12
2 10 2016-5-12
1 11 2016-6-12
2 12 2016-8-12
3 12 2016-8-12
2 13 2016-8-12
1 14 2016-9-12
3 14 2016-9-12
3 11 2016-6-12
Expected output is like, (should list only recent 2 quizid entries for all users)
-------------------------------------
UserId | QuizId(AID)|quizendtime(AID)|
--------------------------------------
1 14 2016-9-12
1 11 2016-6-12
2 13 2016-8-12
2 12 2016-8-12
3 14 2016-9-12
3 12 2016-8-12
Any idea's to produce this output.
Using MySQL user defined variables you can accomplish this:
SELECT
t.UserId,
t.`QuizId(AID)`,
t.`quizendtime(AID)`
FROM
(
SELECT
*,
IF(#sameUser = UserId, #a := #a + 1 , #a := 1) row_number,
#sameUser := UserId
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC
) AS t
WHERE t.row_number <= 2
Working Demo
Note: If you want at most x number of entries for each user then change the condition in where clause like below:
WHERE t.row_number <= x
Explanation:
SELECT
*,
IF(#sameUser = UserId, #a := #a + 1 , #a := 1) row_number,
#sameUser := UserId
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC;
This query sorts all the data in ascending order of userId and descending order of quizendtime(AID).
Now take a walk on this (multi) sorted data.
Every time you see a new userId assign a row_number (1). If you see the same user again then just increase the row_number.
Finally filtering only those records which are having row_number <= 2 ensures the at most two latest entries for each user.
EDIT: As Gordon pointed out that the evaluation of expressions using user defined variables in mysql is not guaranteed to follow the same order always so based on that the above query is slightly modified:
SELECT
t.UserId,
t.`QuizId(AID)`,
t.`quizendtime(AID)`
FROM
(
SELECT
*,
IF (
#sameUser = UserId,
#a := #a + 1,
IF(#sameUser := UserId, #a := 1, #a:= 1)
)AS row_number
FROM your_table
CROSS JOIN (SELECT #a := 1, #sameUser := 0) var
ORDER BY UserId , `quizendtime(AID)` DESC
) AS t
WHERE t.row_number <= 2;
WORKING DEMO V2
User-defined variables are the key to the solution. But, it is very important to have all the variable assignments in a single expression. MySQL does not guarantee the order of evaluation of expressions in a select -- and, in fact, sometimes processes them in different orders.
select t.*
from (select t.*,
(#rn := if(#u = UserId, #rn + 1,
if(#u := UserId, 1, 1)
)
) as rn
from t cross join
(select #u := -1, #rn := 0) params
order by UserId, quizendtime desc
) t
where rn <= 2;
When i want to get row number 5, i do this:
SELECT *
FROM table
ORDER BY id DESC
LIMIT 4, 1
What should my query be, if i want to get row number 5 and 7?
Here is one method:
(SELECT * FROM table ORDER BY id DESC LIMIT 4, 1)
UNION ALL
(SELECT * FROM table ORDER BY id DESC LIMIT 6, 1)
If you don't have an index on id (and even in some cases where you do), a more efficient method would use variables:
SELECT t.*
FROM (SELECT t.*, (#rn := #rn + 1) as rn
FROM table CROSS JOIN (SELECT #rn := 0) params
ORDER BY id DESC
) t
WHERE rn IN (5, 7);
This only sorts the data once.
I'm trying to select first row then skip X next rows then select rest in one query. For example if I have (a,b,c,d,e) in table I need to select "a" (first row) then skip X=2 rows ("b", "c") and then select rest which is "d" and "e", all in one query. So the result would be a,d,e
Try
select *
from
(
select *, #rank := #rank + 1 as rank
from your_table
cross join (select #rank := 0) r
order by colA
) tmp
where rank = 1
or rank > 3
or
select * from your_table
order by colA
limit 1
union all
select * from your_table
order by colA
limit 4, 9999999
You can use a variable to generate a row number:
select
YourField,
YourOtherField
from
(
select id,
YourField,
YourOtherField,
#row := #row + 1 as rownum
from YourTable
cross join (select #row:=0) c
order by YourField -- The field you want to sort by when you say 'first' and 'fourth'
) d
where
rownum = 1 or rownum >= 4
I have table called "users" and need to select 2 rows before and after specific row, sorted by users.score ASC
users table (structure):
id name score
1 John 2
2 Sara 1
3 san 3
4 test 2
5 jery 5
6 simon 6
7 bob2 7
8 jack 4
9 man 2
for example: need to select 2 rows before and after users.id = 5 order by users.score
result should be like:
id name score
3 san 3
8 jack 4
5 jery 5
6 simon 6
7 bob2 7
thanks,
Using union all and subqueries to limit the records should do it:
select * from users where id = 5
union all (
select * from users
where score < (select score from users where id = 5)
order by score desc limit 2
)
union all (
select * from users
where score > (select score from users where id = 5)
order by score asc limit 2
)
order by score
Sample SQL Fiddle
Edit: I think a better method is to number the rows according to score and then select the rows with number -2 and +2 from the rows of id 5:
select id, name, score
from (select
t.*, #rownum1 := #rownum1 + 1 as rank
from users t, (select #rownum1 := 0) r
order by score
) a,
(select rank from (
select t.*,
#rownum := #rownum + 1 as rank
from users t, (select #rownum := 0) r
order by score
) t
where id = 5
) b
where b.rank between a.rank -2 and a.rank+2
order by score;
Sample SQL Fiddle
Perhaps using union all
(
select * from users where id < 5 order by score limit 2
)
union all
(
select * from users where id > 5 order by score limit 2
)
(SELECT x.* FROM users x JOIN users y ON y.score <= x. score WHERE y.id = 5 ORDER BY score LIMIT 3)
UNION
(SELECT x.* FROM users x JOIN users y ON y.score >= x. score WHERE y.id = 5 ORDER BY score DESc LIMIT 3)
[ORDER BY score] ;
http://www.sqlfiddle.com/#!9/45c22/42
I just write the query, based on "jpw" solution (many thanks to him)
select * from users where id = 5
union all (
select * from users
where id in (select id from users where score < (select score from users u where u.id = 5) order by score ASC)
order by score desc limit 2
)
union all (
select * from users
where id in (select id from users where score > (select score from users u where u.id = 5) order by score ASC)
order by score ASC limit 2
)
order by score
Selecting arbitrarily ordered rows before and after a specific id
SET #j = 0;
SET #i = 0;
SELECT *
FROM (
SELECT id, col1, col2, ..., #j:=#j+1 AS pos
FROM `table`
WHERE col1=... ORDER BY col1 DESC, col2 ASC
) AS zz
WHERE (
SELECT position
FROM (
SELECT id AS id2, #i:=#i+1 AS position
FROM `table`
WHERE col1=... ORDER BY col1 DESC, col2 ASC
) AS zz
WHERE id2=$currId
)
IN (pos-5,pos-4,pos-3,pos-2,pos-1,pos,pos+1,pos+2,pos+3,pos+4,pos+5)