I have an issue with a SQl Query. It's as below.
In a particular field the record consists of "A" and "B" only.
Now if I want to find 2 records of "A" followed by 2 records of "B" and then again 2 Records of "A" and 2 records of "B" and so on till the end of records.
example output should be something like below.
ID Field
--------- -----
2 A
3 A
1 B
5 B
4 A
7 A
6 B
8 B
.........
.........
.............. and so on
Kindly help me with the above....as am stuck for this query.
Thanks!
You can do this by enumerating the rows for each value and then cleverly ordering the results:
select id, field
from (select t.*,
if(field = 'A', #a_rn := #a_rn + 1, #b_rn := #b_rn + 1) as rn
from table t
(select #a_rn := 0, #b_rn := 0) vars
) t
order by (rn - 1) div 2, field;
or slower but cooler...
SELECT x.*
FROM my_table x
JOIN my_table y
ON y.field = x.field
AND y.id <= x.id
GROUP
BY field
, id
ORDER
BY CEILING(COUNT(*)/2)
, field;
Related
Is there a way to select frist 3 rows and after that next 3 ( offset 3 ) and get the result as two arrays in a single query ? Something like:
(SELECT * FROM product WHERE 1 LIMIT 3) as first_array
(SELECT * FROM product WHERE 1 OFFSET 3 LIMIT 3) as second_array
Hope you understand me. Sorry about the explanation just dont't know how to explain in other way.
Lets say I only want the ids - output example:
id_1 id_2
1 4
2 5
3 6
What I have tried from the answers below the post is :
SELECT id as id_1 FROM `ct_product` WHERE 1 LIMIT 3
UNION ALL
SELECT id as id_2 FROM `ct_product` WHERE 1 LIMIT 3 OFFSET 3
The result is strange for me. It seems it returns only the second query results and they are not the 4th 5th and 6th row but the 5th 6th and 3th (in this order).
My table rows are:
id
1
2
3
4
5
6
7
You could do it with this query:
SELECT a1.id, a2.id
FROM (SELECT *, #rownum1:=#rownum1+1 AS rownum
FROM (SELECT id
FROM `ct_product`
LIMIT 3
) art
JOIN (SELECT #rownum1 := 0) r
) a1
JOIN (SELECT *, #rownum2:=#rownum2+1 AS rownum
FROM (SELECT id
FROM `ct_product`
LIMIT 3, 3
) art
JOIN (SELECT #rownum2 := 0) r
) a2
ON a1.rownum = a2.rownum
Output:
id id
1 4
2 5
3 6
This query works by creating two new tables with artificially generated row numbers (#rownum1 and #rownum2) from the first 3 and the second 3 rows in the original table. They are then JOINed on matching row numbers to get the desired result.
I have the following data:
id userid name group
1 1 A x
2 1 A y
3 1 A z
4 2 B x
5 2 B y
6 3 C y
7 4 D x
8 5 E x
9 5 E z
10 6 F x
I want to find those records that meet all this condition:
Select all rows where the a userid belongs to a group other than y but the userid also belongs to group y.
The resulting dataset will be as follows:
id userid name group
1 1 A x
3 1 A z
4 2 B x
If you see, it has resulted in two records for userid a because these are two two records belong to groups other than y but the userid 1 also belongs to group y. Same for userid 2.
I have been breaking my head on how to get this in an SQL statement but not even close to a solution.
Any help is appreciated.
Use a join:
SELECT t1.*
FROM mytable t1
INNER JOIN mytable t2
ON t1.user_id = t2.user_id AND t1.group <> t2.group AND t2.group = 'y'
I think that would be the fastest query (but please feel free to try the other solutions as well).
Add an index on user_id if not already there and maybe play with some other indexes as well (maybe a composite index on group and user_id can be utilized)
Use exists
select *
from MyTable a2
where name_group <> 'y'
and exists (select 1
from MyTable a2
where a2.name_group = 'y'
and a2.userid = a1.userid)
You can get all the users that meet the condition using aggregation and having:
select userid
from t
group by userid
having sum( group = 'y' ) > 0 and
sum( group <> 'y') > 0;
I leave it to your to put this into a query to get all the original rows.
I have a table department_courses with following structure :
id department_id name
-- ------------- -----
1 11 Abcd
2 11 Bghg
3 11 Lopps
4 13 Abvgf
So from this table I need to count the position of the subquery. I mean to say , The position of the name Lopps for department_id is 3 . How to get this in mysql query?
If you only need to do this for one row, then a single query is simpler:
select count(*)
from department_courses dc
where dc.id <= (select dc2.id
from department_courses dc2
where dc2.name = 'Lopps'
);
If you want to assign a row number to all rows, then variables are probably a better method.
Try:
select row_num
from (
select t.*, #r := #r + 1 row_num
from department_courses t,
(select #r := 0) r
) x
where x.name = 'Lopps'
x.department_id = 3
I currently have a query that counts the 'parent_id' value for each row and adds it within each row.
For example, if I have 4 records that have the has the value '1432' under 'parent_id' it will show the count value 4 under the 'count' column.
I am trying to limit the amount of rows based on the count number.
For example, let's say we want to exceed the number of records per 'parent_id' to 2. if the 'parent_id' has reached the third record, it just passes on and it won't return that record.
Example of existing table:
ID parent_id count(parent_id)
1 1234 2
2 1234 2
3 3221 3
4 3221 3
5 3221 3
6 5432 1
7 4312 1
The result I'd like to get is:
ID parent_id count(parent_id)
1 1234 2
2 1234 2
3 3221 2
4 3221 2
5 5432 1
6 4312 1
This is a select per group query:
SELECT id, parent_id, rn
FROM (
SELECT #rn:=CASE WHEN #parent_id=parent_id
THEN #rn+1
ELSE 1
END AS rn
, #parent_id:=parent_id AS parent_id
, id
FROM t, (SELECT #rn:=0,#parent_id:='') AS u
ORDER BY parent_id,id
) as s
WHERE rn <= 2
FIDDLE
Mihai's answer may work, but it is not guaranteed to work. The problem is that MySQL does not guarantee the order of evaluation of expressions in the select. And, there are even occasions where it does not evaluate them in the expected order.
So, when using variables, it is safest to put all assignments in a single expression:
SELECT id, parent_id, rn
FROM (SELECT (#rn := if(#parent_id = parent_id, #rn + 1,
if(#parent_id := parent_id, 1, 1)
)
) as rn,
t.*
FROM t CROSS JOIN
(SELECT #rn := 0, #parent_id := '') params
ORDER BY parent_id, id
) t
WHERE rn <= 2;
For example, in this table:
n id num
1 10 100
2 11 60
3 10 20
4 10 20
5 11 10
How do I subtract all the values of num (from top to bottom) with id = 10?
The first value of num in id=10 is subtracted to the 2nd value of num in id = 10 and the answer is subtracted to the third value of num in id = 10 (an so on and so forth if there are n numbers of num with the id =10)
It should display this:
difference of id = 10
50
Here is the working code you need:
SELECT AA.ID, (num_duo-total_sum) as num_diff FROM
(SELECT id, 2*num as num_duo, MIN(n) FROM t1 GROUP BY id ) AA LEFT JOIN
(SELECT id, SUM(num) as total_sum FROM t1 GROUP BY id) BB ON BB.id = AA.id
SQL FIDDLE
If I understand correctly, you want to take the first value for the given id and then subtract subsequent values. "first" is defined by the first column, n.
If so, then this might help:
select sum(case when t.n = f.firstn then num else - num end)
from table t cross join
(select min(n) as firstn
from table t
where id = 10
) f
where id = 10;
Here is a SQL Fiddle.