Say I have column A, B and Date, and I want all rows which are duplicated in A to be removed, while keeping the one with the most recent Date. How would I do this?
I have looked at many other solutions but none seem to work for my case.
Thanks in advance for any help
This should work for you:
DELETE FROM YourTable USING
(SELECT colA, MAX(Date) maxDate
FROM YourTable
GROUP BY colA
) AS Keep
WHERE Keep.maxDate <> YourTable.Date
AND Keep.ColA = YourTable.ColA
will stay:
t=# with sample(a,b,dat) as (values(1,1,1),(1,1,2),(1,2,3),(2,2,3),(2,2,4))
, comparison as (select *,max(dat) over (partition by a) from sample)
select *
from comparison
where dat = max;
a | b | dat | max
---+---+-----+-----
1 | 2 | 3 | 3
2 | 2 | 4 | 4
(2 rows)
and thus to be deleted:
t=# with sample(a,b,dat) as (values(1,1,1),(1,1,2),(1,2,3),(2,2,3),(2,2,4))
, comparison as (select *,max(dat) over (partition by a) from sample)
delete
from comparison
where dat <> max
returning *;
a | b | dat | max
---+---+-----+-----
1 | 1 | 1 | 3
1 | 1 | 2 | 3
2 | 2 | 3 | 4
(3 rows)
of course instead of comparison you should name your table
Related
Hi I'm a new learner of SQL. How can I realize this process in SQL or perhaps with python if needed:
First, from table1, I randomly selected two results:
SELECT TOP 2 id, date
FROM table 1
WHERE date >= 2 AND date <= 6
ORDER BY RAND(CHECKSUM(*) * RAND())
+-----------+
| table1 |
+-----------+
| id | date |
+----+------+
| x | 3 |
| y | 4 |
+----+------+
I need to use the value x and y as conditions to display another table. For instance, using x, I can:
SELECT id, date
FROM table1
WHERE date >= 2 AND date <= 6 AND id = 'x'
ORDER BY date ASC
+-----------+
| table2 |
+-----------+
| id | date |
+----+------+
| x | 3 |
| x | 4 |
| x | 5 |
| x | 6 |
| x | 6 |
+----+------+
What I need is to get the length of table2 without duplication on date. For instance, table2 has 5 rows, but last two duplicate in date. So the final answer is 4 rows.
For id = y, I have to do the same thing (say table3) and compare the length of table3 and table2 to see if consistent.
If yes, then return the length (say, 4 rows); If no, then go back to table1 and select another two id (say, z and y).
I was thinking to use python to select value or create variables, then use python variables in SQL. But it is too much for a new learner. I really appreciate it if someone could help me out this process.
You can use subqueries with IN clause
Here is too a Version with two diemsnions, maybe this will help also
CREATE TABLE table1 ([id] varchar(2),[date] int)
GO
✓
SELECT id, date FROM table1
where date >= 2 and date <= 6
and id IN (
SELECT TOP 2 id FROM table1
WHERE date >= 2 and date <= 6
ORDER BY RAND(CHECKSUM(*) * RAND())
)
ORDER BY date ASC
GO
id | date
:- | ---:
SELECT id, date FROM table1
WHERE EXISTS (SELECT 1
FROM (
SELECT TOP 2 id,[date] FROM table1
WHERE date >= 2 and date <= 6
ORDER BY RAND(CHECKSUM(*) * RAND())) AS table2
WHERE table1.[id] = table2.[id]
AND table1.[date] = table2.[date])
GO
id | date
:- | ---:
db<>fiddle here
I have a table structure with columns similar to the following:
ID | line | value
1 | 1 | 10
1 | 2 | 5
2 | 1 | 6
3 | 1 | 7
3 | 2 | 4
ideally, i'd like to pull the following:
ID | value
1 | 5
2 | 6
3 | 4
one solution would be to do something like the following:
select a.ID, a.value
from
myTable a
inner join (select id, max(line) as line from myTable group by id) b
on a.id = b.id and a.line = b.line
Given the size of the table and that this is just a part of a larger pull, I'd like to see if there's a more elegant / simpler way of pulling this directly.
This is a task for OLAP-functions:
select *
from myTable a
qualify
rank() -- assign a rank for each id
over (partition by id
order by line desc) = 1
Might return multiple rows per id if they share the same max line. If you want to return only one of them, add another column to the order by to make it unique or switch to row_number to get an indeterminate row.
I am having trouble finding a good solution to a problem in SQL.
Say I have table like this:
ID | A | A
--------------------
4427 | 2 | 3
4427 | 3 | 2
4427 | 3 | 5
4427 | 5 | 3
4427 | 1 | 3
4427 | 2 | 5
4427 | 3 | 1
Now I want to find the rows with a unique combination of ID and A. By this I mean that I only want to see the rows where the combination of A(1) and A(2) exists only once. For example the first two rows in the table is "the same" since the combination of 2 and 3 is the same as 3 and 2.
The expected result to my quesion would be:
ID | A | A
--------------------
4427 | 2 | 3
4427 | 3 | 5
4427 | 1 | 3
4427 | 2 | 5
I am using SQL Server 2008.
If I understand correctly, this would be a simple "distinct" query if you ALWAYS had the ColA with a value less then ColB. Given this, you can use a case statement to handle this, combined with a distinct operator.
Try this.
Select Distinct
ID,
Case When ColA < ColB Then ColA Else ColB End,
Case When ColA < ColB Then ColB Else ColA End
From YourTableHere
One way to do this. FYI, the output A1/A2 may have differnet order than original value. If you don't care the order, you may try this.
WITH cte AS (
SELECT ID,A1 AS A, ROW_NUMBER() OVER (ORDER BY A1,A2) AS rn FROM Table1
UNION ALL
SELECT ID,A2 AS A, ROW_NUMBER() OVER (ORDER BY A1,A2) AS rn FROM Table1
)
SELECT DISTINCT ID, MIN(A) AS A1, MAX(A) AS A2
FROM cte
GROUP BY ID, rn
SQL Fiddle
I am attempting to select distinct (last updated) rows from a table in my database. I am trying to get the last updated row for each "Sub section". However I cannot find a way to achieve this.
The table looks like:
ID | Name |LastUpdated | Section | Sub |
1 | Name1 | 2013-04-07 16:38:18.837 | 1 | 1 |
2 | Name2 | 2013-04-07 15:38:18.837 | 1 | 2 |
3 | Name3 | 2013-04-07 12:38:18.837 | 1 | 1 |
4 | Name4 | 2013-04-07 13:38:18.837 | 1 | 3 |
5 | Name5 | 2013-04-07 17:38:18.837 | 1 | 3 |
What I am trying to get my SQL Statement to do is return rows:
1, 2, and 5.
They are distinct for the Sub, and the most recent.
I have tried:
SELECT DISTINCT Sub, LastUpdated, Name
FROM TABLE
WHERE LastUpdated = (SELECT MAX(LastUpdated) FROM TABLE WHERE Section = 1)
Which only returns the distinct row for the most recent updated Row. Which makes sense.
I have googled what I am trying, and checked relevant posts on here. However not managed to find one which really answers what I am trying.
You can use the row_number() window function to assign numbers for each partition of rows with the same value of Sub. Using order by LastUpdated desc, the row with row number one will be the latest row:
select *
from (
select row_number() over (
partition by Sub
order by LastUpdated desc) as rn
, *
from YourTable
) as SubQueryAlias
where rn = 1
Wouldn't it be enough to use group by?
SELECT DISTINCT MIN(Sub), MAX(LastUpdated), MIN(NAME) FROM TABLE GROUP BY Sub Where Section = 1
The problem I'm trying to solve is that I have a table like this:
a and b refer to point on a different table. distance is the distance between the points.
| id | a_id | b_id | distance | delete |
| 1 | 1 | 1 | 1 | 0 |
| 2 | 1 | 2 | 0.2345 | 0 |
| 3 | 1 | 3 | 100 | 0 |
| 4 | 2 | 1 | 1343.2 | 0 |
| 5 | 2 | 2 | 0.45 | 0 |
| 6 | 2 | 3 | 110 | 0 |
....
The important column I'm looking is a_id. If I wanted to keep the closet b for each a, I could do something like this:
update mytable set delete = 1 from (select a_id, min(distance) as dist from table group by a_id) as x where a_gid = a_gid and distance > dist;
delete from mytable where delete = 1;
Which would give me a result table like this:
| id | a_id | b_id | distance | delete |
| 1 | 1 | 1 | 1 | 0 |
| 5 | 2 | 2 | 0.45 | 0 |
....
i.e. I need one row for each value of a_id, and that row should have the lowest value of distance for each a_id.
However I want to keep the 10 closest points for each a_gid. I could do this with a plpgsql function but I'm curious if there is a more SQL-y way.
min() and max() return the smallest and largest, if there was an aggregate function like nth(), which'd return the nth largest/smallest value then I could do this in similar manner to the above.
I'm using PostgeSQL.
Try this:
SELECT *
FROM (
SELECT a_id, (
SELECT b_id
FROM mytable mib
WHERE mib.a_id = ma.a_id
ORDER BY
dist DESC
LIMIT 1 OFFSET s
) AS b_id
FROM (
SELECT DISTINCT a_id
FROM mytable mia
) ma, generate_series (1, 10) s
) ab
WHERE b_id IS NOT NULL
Checked on PostgreSQL 8.3
I love postgres, so it took it as a challenge the second I saw this question.
So, for the table:
Table "pg_temp_29.foo"
Column | Type | Modifiers
--------+---------+-----------
value | integer |
With the values:
SELECT value FROM foo ORDER BY value;
value
-------
0
1
2
3
4
5
6
7
8
9
14
20
32
(13 rows)
You can do a:
SELECT value FROM foo ORDER BY value DESC LIMIT 1 OFFSET X
Where X = 0 for the highest value, 1 for the second highest, 2... And so forth.
This can be further embedded in a subquery to retrieve the value needed. So, to use the dataset provided in the original question we can get the a_ids with the top ten lowest distances by doing:
SELECT a_id, distance FROM mytable
WHERE id IN
(SELECT id FROM mytable WHERE t1.a_id = t2.a_id
ORDER BY distance LIMIT 10);
ORDER BY a_id, distance;
a_id | distance
------+----------
1 | 0.2345
1 | 1
1 | 100
2 | 0.45
2 | 110
2 | 1342.2
Does PostgreSQL have the analytic function rank()? If so try:
select a_id, b_id, distance
from
( select a_id, b_id, distance, rank() over (partition by a_id order by distance) rnk
from mytable
) where rnk <= 10;
This SQL should find you the Nth lowest salary should work in SQL Server, MySQL, DB2, Oracle, Teradata, and almost any other RDBMS: (note: low performance because of subquery)
SELECT * /*This is the outer query part */
FROM mytable tbl1
WHERE (N-1) = ( /* Subquery starts here */
SELECT COUNT(DISTINCT(tbl2.distance))
FROM mytable tbl2
WHERE tbl2.distance < tbl1.distance)
The most important thing to understand in the query above is that the subquery is evaluated each and every time a row is processed by the outer query. In other words, the inner query can not be processed independently of the outer query since the inner query uses the tbl1 value as well.
In order to find the Nth lowest value, we just find the value that has exactly N-1 values lower than itself.