I am comparing from different table to get the COLUMN_NAME of the MAXIMUM value
Examples.
These are example tables: Fruit_tb, Vegetable_tb, State_tb, Foods_tb
Under Fruit_tb
fr_id fruit_one fruit_two
1 20 50
Under Vegetables_tb (v = Vegetables)
v_id v_one V_two
1 10 9
Under State_tb
stateid stateOne stateTwo
1 70 87
Under Food_tb
foodid foodOne foodTwo
1 10 3
Now here is the scenario, I want to get the COLUMN NAMES of the max or greatest value in each table.
You can maybe find out the row which contains the max value of a column. For eg:
SELECT fr_id , MAX(fruit_one) FROM Fruit_tb GROUP BY fr_id;
In order to find the out the max value of a table:
SELECT fr_id ,fruit_one FROM Fruit_tb WHERE fruit_one<(SELECT max(fruit_one ) from Fruit_tb) ORDER BY fr_id DESC limit 1;
A follow up SO for the above scenario.
Maybe you can use GREATEST in order to get the column name which has the max value. But then what I'm not sure is whether you'll be able to retrieve all the columns of different tables at once. You can do something like this to retrieve from a single table:
SELECT CASE GREATEST(`id`,`fr_id`)
WHEN `id` THEN `id`
WHEN `fr_id` THEN `fr_id`
ELSE 0
END AS maxcol,
GREATEST(`id`,`fr_id`) as maxvalue FROM Fruit_tb;
Maybe this SO could help you. Hope it helps!
Related
I'm trying to solve this problem:
I have a query/view that will join ~10 tables to extract some fields for a report (if any). The query doesn't use any grouping function, only joins and cut off some unuseful data.
I have to take this one big view, get the group for the first index, take the max of a date in the second column and take all the information from other fields referring the record of the max value.
I cannot be able to to this in postgres.
As a pseudo code I can give this:
select 1
, max(2)
, 3 referred to the record from max(2)
, 4 referred to the record from max(2)
, ...
, 20 referred to the record from max(2)
from (ViewWithAllJoins) a
group by 1
For privacy and business problem I had to obfuscate some informations, 1/2/3/4... are the name of the column from the view "ViewWithAllJoins", I hope that the problem is still understandable and resolvable!
I've tryied with WINDOW command as reported in Convert keep dense_rank from Oracle query into postgres but I cannot be able to use the group by that I need. Other tryes that I've done was about the dense_rank like shown in Dense_rank first Oracle to Postgresql convert but I can't do any assumption on the order of the data in any of the other fields in exception of 1 and 2, so I can't use any of the aggregate function on them.
Any ideas? Possibly without adding too much subqueryes.
Thank you!
EDIT:
As suggested I'll add some synthetic data to better understand the problem and what I want.
Start:
ID DATE COLUMN1 COLUMN2 COLUMN3
=====================================================================
88888888;"2016-04-02 09:00:00";"aaaaaaaaaaa";"TEXT89" ; 999999999
88888888;"2018-08-21 09:00:00";"a" ;"TEXT1" ; 988888888
88888888;"2017-11-09 09:00:00";"zzzz" ;"TEXT80000" ; 850580582
75858585;"2017-01-31 09:00:00";"~~~~~~~~~~~";"TEXT10" ; 101010101
75858585;"2018-04-02 09:00:00";"eeeeeeeeeee";"TEXT1000" ; 111111111
99999999;"2016-04-02 09:00:00";"8d2ecafd866";"TEXT808911"; 777777777
What I want:
ID DATE COLUMN1 COLUMN2 COLUMN3
===================================================================
88888888;"2018-08-21 09:00:00";"a" ;"TEXT1" ; 988888888
75858585;"2018-04-02 09:00:00";"eeeeeeeeeee";"TEXT1000" ; 111111111
99999999;"2016-04-02 09:00:00";"8d2ecafd866";"TEXT808911"; 777777777
So the group by id, the max of the date and the other fields related to the row of the max date.
-- So you have duplicate records per ID, and for every ID you want to select the record with the most recent date ?
Use NOT EXISTS:
SELECT id,zdate,column1,column2,column3 -- , ...
FROM queryview t
WHERE NOT EXISTS (
SELECT *
FROM queryview x
WHERE x.id=t.id
AND x.zdate > t.zdate
);
Or, use row_number() over a window, and pick only the row with the final date:
SELECT id,zdate,column1,column2,column3 -- , ...
FROM ( SELECT *
, row_number() OVER(PARTITION BY id, ORDER BY zdate DESC) AS rn
FROM queryview
) q
WHERE q.rn = 1
;
id datetime new_column datetime_rankx
1 12.01.2015 18:10:10 12.01.2015 18:10:10 1
2 03.12.2014 14:44:57 03.12.2014 14:44:57 1
2 21.11.2015 11:11:11 03.12.2014 14:44:57 2
3 01.01.2011 12:12:12 01.01.2011 12:12:12 1
3 02.02.2012 13:13:13 01.01.2011 12:12:12 2
3 03.03.2013 14:14:14 01.01.2011 12:12:12 3
I want to make new column, which will have minimum datetime value for each row in group by id.
How could I do it in Power BI desktop using DAX query?
Use this expression:
NewColumn =
CALCULATE(
MIN(
Table[datetime]),
FILTER(Table,Table[id]=EARLIER(Table[id])
)
)
In Power BI using a table with your data it will produce this:
UPDATE: Explanation and EARLIER function usage.
Basically, EARLIER function will give you access to values of different row context.
When you use CALCULATE function it creates a row context of the whole table, theoretically it iterates over every table row. The same happens when you use FILTER function it will iterate on the whole table and evaluate every row against the filter condition.
So far we have two row contexts, the row context created by CALCULATE and the row context created by FILTER. Note FILTER use the EARLIER to get access to the CALCULATE's row context. Having said that, in our case for every row in the outer (CALCULATE's row context) the FILTER returns a set of rows that correspond to the current id in the outer context.
If you have a programming background it could give you some sense. It is similar to a nested loop.
Hope this Python code points the main idea behind this:
outer_context = ['row1','row2','row3','row4']
inner_context = ['row1','row2','row3','row4']
for outer_row in outer_context:
for inner_row in inner_context:
if inner_row == outer_row: #this line is what the FILTER and EARLIER do
#Calculate the min datetime using the filtered rows
...
...
UPDATE 2: Adding a ranking column.
To get the desired rank you can use this expression:
RankColumn =
RANKX(
CALCULATETABLE(Table,ALLEXCEPT(Table,Table[id]))
,Table[datetime]
,Hoja1[datetime]
,1
)
This is the table with the rank column:
Let me know if this helps.
I need to divide with UPDATE command rows (selected from subselect) in PostgreSQL table into groups, these groups will be identified with integer value in one of its columns. These groups should be with the same size. Source table contains billions of records.
For example I need to divide 213 selected rows into groups, every group should contains 50 records. The result will be:
1 - 50. row => 1
51 - 100. row => 2
101 - 150. row => 3
151 - 200. row => 4
200 - 213. row => 5
There is no problem to do it with some loop (or use PostgreSQL window functions), but I need to do it very efficiently and quickly. I can't use sequence in id because there should be gaps in these ids.
I have an idea to use random integer number generator and set it as default value for a row. But this is not useable when I need to adjust group size.
The query below should display 213 rows with a group-number from 0-4. Just add 1 if you want 1-5
SELECT i, (row_number() OVER () - 1) / 50 AS grp
FROM generate_series(1001,1213) i
ORDER BY i;
create temporary sequence s minvalue 0 start with 0;
select *, nextval('s') / 50 grp
from t;
drop sequence s;
I think it has the potential to be faster than the row_number version #Richard. But the difference could be not relevant depending on the specifics.
I have a table where I store information about users. The table has the following structure:
CREATE TABLE PERSONS
(
ID NUMBER(20, 0) NOT NULL,
FIRSTNAME VARCHAR2(40),
LASTNAME VARCHAR2(40),
BIRTHDAY DATE,
CONSTRAINT PERSONEN_PK PRIMARY KEY
(ID)
ENABLE
);
After inserting some test data:
SET DEFINE OFF;
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values ('1','Max','Mustermann',to_date('31.10.89','DD.MM.RR'));
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values ('2','Max','Mustermann',to_date('31.10.89','DD.MM.RR'));
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values ('3','Carl','Carlchen',to_date('01.01.12','DD.MM.RR'));
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values ('4','Max','Mustermann',to_date('31.10.89','DD.MM.RR'));
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values ('5','Max','Mustermann',to_date('31.10.89','DD.MM.RR'));
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values ('6','Carl','Carlchen',to_date('01.01.12','DD.MM.RR'));
I want to select all duplicates of a given user. Let's use "Max Mustermann" for example:
SELECT p.id,p.firstname,p.lastname,p.birthday
FROM persons p
WHERE p.firstname = 'Max'
AND p.lastname = 'Mustermann'
AND p.birthday = to_date('31.10.1989','dd.mm.yyyy')
ORDER BY p.firstname,p.lastname;
This gives me a result like this:
id first last birthday
=================================
1 Max Mustermann 31.10.89
2 Max Mustermann 31.10.89
4 Max Mustermann 31.10.89
5 Max Mustermann 31.10.89
I want to do a case insensitive compare, so I change the query using lower (and trim) like this:
SELECT p.id,p.firstname,p.lastname,p.birthday
FROM persons p
WHERE lower(trim(p.firstname)) = lower(trim('mAx '))
AND lower(trim(p.lastname)) = lower(trim(' musteRmann '))
AND p.birthday = to_date('31.10.1989','dd.mm.yyyy')
ORDER BY p.lastname,p.firstname;
Now surprise the order has changed!
id first last birthday
=================================
1 Max Mustermann 31.10.89
5 Max Mustermann 31.10.89
4 Max Mustermann 31.10.89
2 Max Mustermann 31.10.89
Why does the order change, just by using lower() (same result when using without trim())!? I can get a stable ordering by adding the id column to the ORDER BY. But shouldn't the lower() have no affect to the ordering?
Workaround by also using id column for ORDER BY:
SELECT p.id,p.firstname,p.lastname,p.birthday
FROM persons p
WHERE p.firstname = 'Max'
AND p.lastname = 'Mustermann'
AND p.birthday = to_date('31.10.1989','dd.mm.yyyy')
ORDER BY p.firstname,p.lastname,p.id;
SELECT p.id,p.firstname,p.lastname,p.birthday
FROM persons p
WHERE lower(trim(p.firstname)) = lower(trim('mAx '))
AND lower(trim(p.lastname)) = lower(trim(' musteRmann '))
AND p.birthday = to_date('31.10.1989','dd.mm.yyyy')
ORDER BY p.lastname,p.firstname,p.id;
If the values to be ordered by are identical, then the DBMS is free to choose any order it feels correct (the same way it is free to choose any order if no order by is specified alltogether).
Because all values of the columns in the order by are identical the resulting order is not stable. The only way to get a stable order is to include a unique column as an additional order criteria for ties - exactly what you did when you added the id column.
Why does the order change, just by using lower()
From a technical point, I'd guess that applying the lower() changed the execution plan and therefor the access path to the data.
But again (just to make sure): ordering on identical values never guarantees a stable order!
There is no ordering without an order by clause. Sometimes it looks like there might be (group by fooled a lot of people in older releases`, but it's only coincidental, and must not be relied upon. In your case you're ordering by some columns, but you expect duplicates within that ordering to be further ordered implicitly, which won't happen - or at least cannot be relied on.
In this case Oracle probably happens to be retrieving the rows for your first query in the order you inserted them purely as a side effect of how it's reading data from the blocks, and the order by sorts them within that set without actually changing them (or quite likely it's skipping the order by step internally if it realises it's pointless; the explain plan would tell you that).
If you change the order the order the records are created:
...
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values
('5','Max','Mustermann',to_date('31.10.89','DD.MM.RR'));
Insert into PERSONS (ID,FIRSTNAME,LASTNAME,BIRTHDAY) values
('4','Max','Mustermann',to_date('31.10.89','DD.MM.RR'));
...
then the result 'order' changes too:
SELECT p.id,p.firstname,p.lastname,p.birthday
FROM persons p
WHERE p.firstname = 'Max'
AND p.lastname = 'Mustermann'
AND p.birthday = to_date('31.10.1989','dd.mm.yyyy')
ORDER BY p.firstname,p.lastname;
ID FIRSTNAME LASTNAME BIRTHDAY
---------- -------------------- -------------------- ---------
1 Max Mustermann 31-OCT-89
2 Max Mustermann 31-OCT-89
5 Max Mustermann 31-OCT-89
4 Max Mustermann 31-OCT-89
Once you have the function things are changing enough for that happy accident to go out of the window, even if the records are inserted in id order (which has no relevance to the DB internally). lower() isn't changing the ordering, you just aren't getting lucky any more.
You cannot expect or rely on an order unless you fully specify it in the order by clause.
I'm trying to find a way to use Perl to further process a PostgreSQL output. If there's a better way to do this via PostgreSQL, please let me know. I basically need to choose certain columns (Realtime, Value) in a file to concatenate certains columns to create a row while keeping ID and CAT.
First time posting, so please let me know if I missed anything.
Input:
ID CAT Realtime Value
A 1 time1 55
A 1 time2 57
B 1 time3 75
C 2 time4 60
C 3 time5 66
C 3 time6 67
Output:
ID CAT Time Values
A 1 time 1,time2 55,57
B 1 time3 75
C 2 time4 60
C 3 time5,time6 66,67
You could do this most simply in Postgres like so (using array columns)
CREATE TEMP TABLE output AS SELECT
id, cat, ARRAY_AGG(realtime) as time, ARRAY_AGG(value) as values
FROM input GROUP BY id, cat;
Then select whatever you want out of the output table.
SELECT id
, cat
, string_agg(realtime, ',') AS realtimes
, string_agg(value, ',') AS values
FROM input
GROUP BY 1, 2
ORDER BY 1, 2;
string_agg() requires PostgreSQL 9.0 or later and concatenates all values to a delimiter-separated string - while array_agg() (v8.4+) creates am array out of the input values.
About 1, 2 - I quote the manual on the SELECT command:
GROUP BY clause
expression can be an input column name, or the name or ordinal number
of an output column (SELECT list item), or ...
ORDER BY clause
Each expression can be the name or ordinal number of an output column
(SELECT list item), or
Emphasis mine. So that's just notational convenience. Especially handy with complex expressions in the SELECT list.