Getting the last updated name - sql

I am having a table having records like this:
+------+------+
| ID | name |
+------+------+
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | A |
| 5 | B |
| 6 | A |
| 7 | A |
| 8 | A |
+------+------+
I need to get value of A after it was last updated from a different value, for example here it would be the row at ID 6.

Try this query (MySQL syntax):
select min(ID)
from records
where name = 'A'
and ID >=
(
select max(ID)
from records
where name <> 'A'
);
Illustration:
select * from records;
+------+------+
| ID | name |
+------+------+
| 1 | A |
| 2 | B |
| 3 | C |
| 4 | A |
| 5 | B |
| 6 | A |
| 7 | A |
| 8 | A |
+------+------+
-- run query:
+---------+
| min(ID) |
+---------+
| 6 |
+---------+

Using the Lag function...
SELECT Max([ID])
FROM (SELECT [name], [ID],
Lag([name]) OVER (ORDER BY [ID]) AS PrvVal
FROM tablename) tbl
WHERE [name] = 'A'
AND prvval <> 'A'
Online Demo: http://www.sqlfiddle.com/#!18/a55eb/2/0
If you want to get the whole row, you can do this...
SELECT Top 1 *
FROM (SELECT [name], [ID],
Lag([name]) OVER (ORDER BY [ID]) AS PrvVal
FROM tablename) tbl
WHERE [name] = 'A' AND prvval <> 'A'
ORDER BY [ID] DESC
Online Demo: http://www.sqlfiddle.com/#!18/a55eb/22/0

The ANSI SQL below uses a self-join on the previous id.
And the where-clause gets those with a name that's different from the previous.
select max(t1.ID) as ID
from YourTable as t1
left join YourTable as t2 on t1.ID = t2.ID+1
where (t1.name <> t2.name or t2.name is null)
and t1.name = 'A';
It should work on most RDBMS, including MS Sql Server.
Note that with the ID+1 that there's an assumption that are no gaps between the ID's.

Related

Grouping data using PostgreSQL based on 2 fields

I have a problem with grouping data in postgresql. let say that I have table called my_table
some_id | description | other_id
---------|-----------------|-----------
1 | description-1 | a
1 | description-2 | b
2 | description-3 | a
2 | description-4 | a
3 | description-5 | a
3 | description-6 | b
3 | description-7 | b
4 | description-8 | a
4 | description-9 | a
4 | description-10 | a
...
I would like to group my database based on some_id then differentiate which one has same and different other_id
I would expecting 2 type of queries: 1 that has same other_id and 1 that has different other_id
Expected result
some_id | description | other_id
---------|-----------------|-----------
2 | description-3 | a
2 | description-4 | a
4 | description-8 | a
4 | description-9 | a
4 | description-10 | a
AND
some_id | description | other_id
---------|-----------------|-----------
1 | description-1 | a
1 | description-2 | b
3 | description-5 | a
3 | description-6 | b
3 | description-7 | b
I am open for suggestion both using sequelize or raw query
thank you
One approach, using MIN and MAX as analytic functions:
WITH cte AS (
SELECT *, MIN(other_id) OVER (PARTITION BY some_id) min_other_id,
MAX(other_id) OVER (PARTITION BY some_id) max_other_id
FROM yourTable
)
-- all some_id the same
SELECT some_id, description, other_id
FROM cte
WHERE min_other_id = max_other_id;
-- not all some_id the same
SELECT some_id, description, other_id
FROM cte
WHERE min_other_id <> max_other_id;
Demo
You can also do this using exists and not exists:
-- all same
select t.*
from my_table t
where not exists (select 1
from my_table t2
where t2.some_id = t.some_id and t2.other_id <> t.other_id
);
-- any different
select t.*
from my_table t
where exists (select 1
from my_table t2
where t2.some_id = t.some_id and t2.other_id <> t.other_id
);
Note that this ignores NULL values. If you want them treated as a "different" value then use is distinct from rather than <>.

How can I subtract two row's values within same column using sql query in access?

(query access)
This is the table structure:
+-----+--------+--------+
| id | name | sub1 |
+-----+--------+--------+
| 1 | ABC | 6.27% |
| 2 | ABC | 7.47% |
| 3 | PQR | 3.39% |
| 4 | PQR | 2.21% |
+-----+--------+--------+
I want to subtract Sub1
Output should be:
+-----+--------+---------+------------------------------------+
| id | name | sub1 | |
+-----+--------+---------+------------------------------------+
| 1 | ABC | 6.27% | 0 First Rec no need Subtract |
| 2 | ABC | 7.47% | 1.2% <=(7.47-6.27) |
| 3 | PQR | 3.39% | 0 First Rec no need Subtract |
| 4 | PQR | 2.21% | -1.18% <=(2.21-3.39) |
+-----+--------+---------+------------------------------------+
Thank you so much.
If you can guarantee consecutive id values, then the following presents an alternative:
select t.*, nz(t.sub1-u.sub1,0) as sub2
from YourTable t left join YourTable u on t.name = u.name and t.id = u.id+1
Change YourTable to the name of your table.
This is painful, but you can do:
select t.*,
(select top 1 t2.sub1
from t as t2
where t2.name = t.name and t2.id < t.id
order by t2.id desc
) as prev_sub1
from t;
This gives the previous value or NULL for the first row. You can just use - for the subtraction.
An index on (name, id) would help a bit with performance. However, if you can upgrade to a better database, you can then just use lag().

How do I select rows with maximum value?

Given this table I want to retrieve for each different url the row with the maximum count. For this table the output should be: 'dell.html' 3, 'lenovo.html' 4, 'toshiba.html' 5
+----------------+-------+
| url | count |
+----------------+-------+
| 'dell.html' | 1 |
| 'dell.html' | 2 |
| 'dell.html' | 3 |
| 'lenovo.html' | 1 |
| 'lenovo.html' | 2 |
| 'lenovo.html' | 3 |
| 'lenovo.html' | 4 |
| 'toshiba.html' | 1 |
| 'toshiba.html' | 2 |
| 'toshiba.html' | 3 |
| 'toshiba.html' | 4 |
| 'toshiba.html' | 5 |
+----------------+-------+
What SQL query do I need to write to do this?
Try to use this query:
select url, max(count) as count
from table_name
group by url;
use aggregate function
select max(count) ,url from table_name group by url
From your comments it seems you need corelated subquery
select t1.* from table_name t1
where t1.count = (select max(count) from table_name t2 where t2.url=t1.url
)
If row_number support on yours sqllite version
then you can write query like below
select * from
(
select *,row_number() over(partition by url order by count desc) rn
from table_name
) a where a.rn=1

Impala - Does impala allow multi GROUP_CONCAT in one query

For example, I have a table below
+-----------+-------+------------+
| Id | a| b|
+-----------+-------+------------+
| 1 | 6 | 20 |
| 1 | 4 | 55 |
| 1 | 9 | 56 |
| 1 | 2 | 67 |
| 1 | 7 | 80 |
| 1 | 5 | 66 |
| 1 | 3 | 33 |
| 1 | 8 | 34 |
| 1 | 1 | 52 |
I want the output would be like below by using Impala
+-----------+-------------------+-----------------------------+
| Id | a | b |
+-----------+-------------------+-----------------------------+
| 1 | 6,4,9,2,7,5,3,8,1 | 20,55,56,67,80,66,33,34,52 |
+-----------+-------------------+-----------------------------+
In Impala, I have used
SELECT Id,
group_concat(DISTINCT a) AS a,
group_concat(DISTINCT b) AS b
FROM table GROUP BY Id
It will always get Syntax error. Just wondering is that we are not allowed to use multi group_concat for one query in Impala? or not allow to use multi Distinct for one query?
From the documentation for GROUP_CONCAT:
You cannot apply the DISTINCT operator to the argument of this function.
But, as workaround, we can use two separate subqueries to find the distinct values:
WITH cte1 AS (
SELECT Id, GROUP_CONCAT(a) AS a
FROM (SELECT DISTINCT Id, a FROM yourTable) t
GROUP BY Id
),
cte2 AS (
SELECT Id, GROUP_CONCAT(b) AS b
FROM (SELECT DISTINCT Id, b FROM yourTable) t
GROUP BY Id
)
SELECT
t1.Id,
t1.a,
t2.b
FROM cte1 t1
INNER JOIN cte2 t2
ON t1.Id = t2.Id;

SELECT only latest record of an ID from given rows

I have this table shown below...How do I select only the latest data of the id based on changeno?
+----+--------------+------------+--------+
| id | data | changeno | |
+----+--------------+------------+--------+
| 1 | Yes | 1 | |
| 2 | Yes | 2 | |
| 2 | Maybe | 3 | |
| 3 | Yes | 4 | |
| 3 | Yes | 5 | |
| 3 | No | 6 | |
| 4 | No | 7 | |
| 5 | Maybe | 8 | |
| 5 | Yes | 9 | |
+----+---------+------------+-------------+
I would want this result...
+----+--------------+------------+--------+
| id | data | changeno | |
+----+--------------+------------+--------+
| 1 | Yes | 1 | |
| 2 | Maybe | 3 | |
| 3 | No | 6 | |
| 4 | No | 7 | |
| 5 | Yes | 9 | |
+----+---------+------------+-------------+
I currently have this SQL statement...
SELECT id, data, MAX(changeno) as changeno FROM Table1 GROUP BY id;
and clearly it doesn't return what I want. This should return an error because of the aggrerate function. If I added fields under the GROUP BY clause it works but it doesn't return what I want. The SQL statement is by far the closest I could think of. I'd appreciate it if anybody could help me on this. Thank you in advance :)
This is typically referred to as the "greatest-n-per-group" problem. One way to solve this in SQL Server 2005 and higher is to use a CTE with a calculated ROW_NUMBER() based on the grouping of the id column, and sorting those by largest changeno first:
;WITH cte AS
(
SELECT id, data, changeno,
rn = ROW_NUMBER() OVER (PARTITION BY id ORDER BY changeno DESC)
FROM dbo.Table1
)
SELECT id, data, changeno
FROM cte
WHERE rn = 1
ORDER BY id;
You want to use row_number() for this:
select id, data, changeno
from (SELECT t.*,
row_number() over (partition by id order by changeno desc) as seqnum
FROM Table1 t
) t
where seqnum = 1;
Not a well formed or performance optimized query but for small tasks it works fine.
SELECT * FROM TEST
WHERE changeno IN (SELECT MAX(changeno)
FROM TEST
GROUP BY id)
for other alternatives :
DECLARE #Table1 TABLE
(
id INT, data VARCHAR(5), changeno INT
);
INSERT INTO #Table1
SELECT 1,'Yes',1
UNION ALL
SELECT 2,'Yes',2
UNION ALL
SELECT 2,'Maybe',3
UNION ALL
SELECT 3,'Yes',4
UNION ALL
SELECT 3,'Yes',5
UNION ALL
SELECT 3,'No',6
UNION ALL
SELECT 4,'No',7
UNION ALL
SELECT 5,'Maybe',8
UNION ALL
SELECT 5,'Yes',9
SELECT Y.id, Y.data, Y.changeno
FROM #Table1 Y
INNER JOIN (
SELECT id, changeno = MAX(changeno)
FROM #Table1
GROUP BY id
) X ON X.id = Y.id
WHERE X.changeno = Y.changeno
ORDER BY Y.id