I would like to get the previous(lag) calculated value?
id | value
-------|-------
1 | 1
2 | 3
3 | 5
4 | 7
5 | 9
What I am trying to achieve is this:
id | value | new value
-------|-------|-----------
1 | 1 | 10 <-- 1 * lag(new_value)
2 | 3 | 30 <-- 3 * lag(new_value)
3 | 5 | 150 <-- 5 * lag(new_value)
4 | 7 | 1050 <-- 7 * lag(new_value)
5 | 9 | 9450 <-- 9 * lag(new_value)
What I have tried:
SELECT value,
COALESCE(lag(new_value) OVER () * value, 10) AS new_value
FROM table
Error:
ERROR: column "new_value" does not exist
Similar to Juan's answer but I thought I'd post it anyway. It at least avoids the need for the ID column and doesn't have the empty row at the end:
with recursive all_data as (
select value, value * 10 as new_value
from data
where value = 1
union all
select c.value,
c.value * p.new_value
from data c
join all_data p on p.value < c.value
where c.value = (select min(d.value)
from data d
where d.value > p.value)
)
select *
from all_data
order by value;
The idea is to join exactly one row in the recursive part to exactly one "parent" row. While the "exactly one parent" can be done with a derived table and a lateral join (which surprisingly does allow the limit). The "exactly one row" from the "child" in the recursive part can unfortunately only be done using the sub-select with a min().
The where c.value= (...) wouldn't be necessary if it was possible to use an order by and limit in the recursive part as well, but unfortunately that is not supported in the current Postgres version.
Online example: http://rextester.com/WFBVM53545
My bad, this isnt that easy as I thought. Got a very close result but still need some tunning.
DEMO
WITH RECURSIVE t(n, v) AS (
SELECT MIN(value), 10
FROM Table1
UNION ALL
SELECT (SELECT min(value) from Table1 WHERE value > n),
(SELECT min(value) from Table1 WHERE value > n) * v
FROM t
JOIN Table1 on t.n = Table1.value
)
SELECT n, v
FROM t;
Related
I have an unusual problem I'm trying to solve with SQL where I need to generate sequential numbers for partitioned rows but override specific numbers with values from the data, while not breaking the sequence (unless the override causes a number to be used greater than the number of rows present).
I feel I might be able to achieve this by selecting the rows where I need to override the generated sequence value and the rows I don't need to override the value, then unioning them together and somehow using coalesce to get the desired dynamically generated sequence value, or maybe there's some way I can utilise recursive.
I've not been able to solve this problem yet, but I've put together a SQL Fiddle which provides a simplified version:
http://sqlfiddle.com/#!17/236b5/5
The desired_dynamic_number is what I'm trying to generate and the generated_dynamic_number is my current work-in-progress attempt.
Any pointers around the best way to achieve the desired_dynamic_number values dynamically?
Update:
I'm almost there using lag:
http://sqlfiddle.com/#!17/236b5/24
step-by-step demo:db<>fiddle
SELECT
*,
COALESCE( -- 3
first_value(override_as_number) OVER w -- 2
, 1
)
+ row_number() OVER w - 1 -- 4, 5
FROM (
SELECT
*,
SUM( -- 1
CASE WHEN override_as_number IS NOT NULL THEN 1 ELSE 0 END
) OVER (PARTITION BY grouped_by ORDER BY secondary_order_by)
as grouped
FROM sample
) s
WINDOW w AS (PARTITION BY grouped_by, grouped ORDER BY secondary_order_by)
Create a new subpartition within your partitions: This cumulative sum creates a unique group id for every group of records which starts with a override_as_number <> NULL followed by NULL records. So, for instance, your (AAA, d) to (AAA, f) belongs to the same subpartition/group.
first_value() gives the first value of such subpartition.
The COALESCE ensures a non-NULL result from the first_value() function if your partition starts with a NULL record.
row_number() - 1 creates a row count within a subpartition, starting with 0.
Adding the first_value() of a subpartition with the row count creates your result: Beginning with the one non-NULL record of a subpartition (adding the 0 row count), the first following NULL records results in the value +1 and so forth.
Below query gives exact result, but you need to verify with all combinations
select c.*,COALESCE(c.override_as_number,c.act) as final FROM
(
select b.*, dense_rank() over(partition by grouped_by order by grouped_by, actual) as act from
(
select a.*,COALESCE(override_as_number,row_num) as actual FROM
(
select grouped_by , secondary_order_by ,
dense_rank() over ( partition by grouped_by order by grouped_by, secondary_order_by ) as row_num
,override_as_number,desired_dynamic_number from fiddle
) a
) b
) c ;
column "final" is the result
grouped_by | secondary_order_by | row_num | override_as_number | desired_dynamic_number | actual | act | final
------------+--------------------+---------+--------------------+------------------------+--------+-----+-------
AAA | a | 1 | 1 | 1 | 1 | 1 | 1
AAA | b | 2 | | 2 | 2 | 2 | 2
AAA | c | 3 | 3 | 3 | 3 | 3 | 3
AAA | d | 4 | 3 | 3 | 3 | 3 | 3
AAA | e | 5 | | 4 | 5 | 4 | 4
AAA | f | 6 | | 5 | 6 | 5 | 5
AAA | g | 7 | 999 | 999 | 999 | 6 | 999
XYZ | a | 1 | | 1 | 1 | 1 | 1
ZZZ | a | 1 | | 1 | 1 | 1 | 1
ZZZ | b | 2 | | 2 | 2 | 2 | 2
(10 rows)
Hope this helps!
The real world problem I was trying to solve did not have a nicely ordered secondary_order_by column, instead it would be something a bit more randomised (a created timestamp).
For the benefit of people who stumble across this question with a similar problem to solve, a colleague solved this problem using a cartesian join, who's solution I'm posting below. The solution is Snowflake SQL which should be possible to adapt to Postgres. It does fall down on higher override_as_number values though unless the from table(generator(rowcount => 1000)) 1000 value is not increased to something suitably high.
The SQL:
with tally_table as (
select row_number() over (order by seq4()) as gen_list
from table(generator(rowcount => 1000))
),
base as (
select *,
IFF(override_as_number IS NULL, row_number() OVER(PARTITION BY grouped_by, override_as_number order by random),override_as_number) as rownum
from "SANDPIT"."TEST"."SAMPLEDATA" order by grouped_by,override_as_number,random
) --select * from base order by grouped_by,random;
,
cart_product as (
select *
from tally_table cross join (Select distinct grouped_by from base ) as distinct_grouped_by
) --select * from cart_product;
,
filter_product as (
select *,
row_number() OVER(partition by cart_product.grouped_by order by cart_product.grouped_by,gen_list) as seq_order
from cart_product
where CONCAT(grouped_by,'~',gen_list) NOT IN (select concat(grouped_by,'~',override_as_number) from base where override_as_number is not null)
) --select * from try2 order by 2,3 ;
select base.grouped_by,
base.random,
base.override_as_number,
base.answer, -- This is hard coded as test data
IFF(override_as_number is null, gen_list, seq_order) as computed_answer
from base inner join filter_product on base.rownum = filter_product.seq_order and base.grouped_by = filter_product.grouped_by
order by base.grouped_by,
random;
In the end I went for a simpler solution using a temporary table and cursor to inject override_as_number values and shuffle other numbers.
To get 2 rows from each group I can use ROW_NUMBER() with condition <= 2 at last but my question is what If I want to get different limits on each group e.g 3 rows for section_id 1, 1 rows for 2 and 1 rows for 3?
Given the following table:
db=# SELECT * FROM xxx;
id | section_id | name
----+------------+------
1 | 1 | A
2 | 1 | B
3 | 1 | C
4 | 1 | D
5 | 2 | E
6 | 2 | F
7 | 3 | G
8 | 2 | H
(8 rows)
I get the first 2 rows (ordered by name) for each section_id, i.e. a result similar to:
id | section_id | name
----+------------+------
1 | 1 | A
2 | 1 | B
5 | 2 | E
6 | 2 | F
7 | 3 | G
(5 rows)
Current Query:
SELECT
*
FROM (
SELECT
ROW_NUMBER() OVER (PARTITION BY section_id ORDER BY name) AS r,
t.*
FROM
xxx t) x
WHERE
x.r <= 2;
Create a table to contain the section limits, then join. The big advantage being that as new sections are required or limits change maintenance is reduced to a single table update and comes at very little cost. See example.
select s.section_id, s.name
from (select section_id, name
, row_number() over (partition by section_id order by name) rn
from sections
) s
left join section_limits sl on (sl.section_id = s.section_id)
where
s.rn <= coalesce(sl.limit_to,2);
Just fix up your where clause:
with numbered as (
select row_number() over (partition by section_id
order by name) as r,
t.*
from xxx t
)
select *
from numbered
where (section_id = 1 and r <= 3)
or (section_id = 2 and r <= 1)
or (section_id = 3 and r <= 1);
I have a PostgreSQL (9.4) table that contains time stamp ranges and user IDs, and I need to collapse any overlapping ranges (with the same user ID) into a single record.
I've tried a complicated set of CTEs to accomplish this, but there are some edge cases in our (40,000+ rows) real table that complicate matters. I've come to the conclusion that I probably need a recursive CTE, but I haven't had any luck writing it.
Here's some code to create a test table and populate it with data. This isn't the exact layout of our table, but it's close enough for an example.
CREATE TABLE public.test
(
id serial,
sessionrange tstzrange,
fk_user_id integer
);
insert into test (sessionrange, fk_user_id)
values
('[2016-01-14 11:57:01-05,2016-01-14 12:06:59-05]', 1)
,('[2016-01-14 12:06:53-05,2016-01-14 12:17:28-05]', 1)
,('[2016-01-14 12:17:24-05,2016-01-14 12:21:56-05]', 1)
,('[2016-01-14 18:18:00-05,2016-01-14 18:42:09-05]', 2)
,('[2016-01-14 18:18:08-05,2016-01-14 18:18:15-05]', 1)
,('[2016-01-14 18:38:12-05,2016-01-14 18:48:20-05]', 1)
,('[2016-01-14 18:18:16-05,2016-01-14 18:18:26-05]', 1)
,('[2016-01-14 18:18:24-05,2016-01-14 18:18:31-05]', 1)
,('[2016-01-14 18:18:12-05,2016-01-14 18:18:20-05]', 3)
,('[2016-01-14 19:32:12-05,2016-01-14 23:18:20-05]', 3)
,('[2016-01-14 18:18:16-05,2016-01-14 18:18:26-05]', 4)
,('[2016-01-14 18:18:24-05,2016-01-14 18:18:31-05]', 2);
I have found that I can do this to get the sessions sorted by the time they started:
select * from test order by fk_user_id, sessionrange
I could use this to determine whether an individual record overlaps with the previous, using window functions:
SELECT *, sessionrange && lag(sessionrange) OVER (PARTITION BY fk_user_id ORDER BY sessionrange)
FROM test
ORDER BY fk_user_id, sessionrange
But this only detects whether the single previous record overlaps the current one (see the record where id = 6). I need to detect all the way back to the beginning of the partition.
After that, I'd need to group any records that overlap together, to find the beginning of the earliest session and the end of the last session to terminate.
I'm sure there's a way to do this that I'm overlooking. How can I collapse these overlapping records?
It is relatively easy to merge overlapping ranges as elements of an array. For simplicity the following function returns set of tstzrange:
create or replace function merge_ranges(tstzrange[])
returns setof tstzrange language plpgsql as $$
declare
t tstzrange;
r tstzrange;
begin
foreach t in array $1 loop
if r && t then r:= r + t;
else
if r notnull then return next r;
end if;
r:= t;
end if;
end loop;
if r notnull then return next r;
end if;
end $$;
Just aggregate the ranges for a user and use the function:
select fk_user_id, merge_ranges(array_agg(sessionrange))
from test
group by 1
order by 1, 2
fk_user_id | merge_ranges
------------+-----------------------------------------------------
1 | ["2016-01-14 17:57:01+01","2016-01-14 18:21:56+01"]
1 | ["2016-01-15 00:18:08+01","2016-01-15 00:18:15+01"]
1 | ["2016-01-15 00:18:16+01","2016-01-15 00:18:31+01"]
1 | ["2016-01-15 00:38:12+01","2016-01-15 00:48:20+01"]
2 | ["2016-01-15 00:18:00+01","2016-01-15 00:42:09+01"]
3 | ["2016-01-15 00:18:12+01","2016-01-15 00:18:20+01"]
3 | ["2016-01-15 01:32:12+01","2016-01-15 05:18:20+01"]
4 | ["2016-01-15 00:18:16+01","2016-01-15 00:18:26+01"]
(8 rows)
Alternatively, the algorithm can be applied to the entire table in one function loop. I'm not sure but for a large dataset this method should be faster.
create or replace function merge_ranges_in_test()
returns setof test language plpgsql as $$
declare
curr test;
prev test;
begin
for curr in
select *
from test
order by fk_user_id, sessionrange
loop
if prev notnull and prev.fk_user_id <> curr.fk_user_id then
return next prev;
prev:= null;
end if;
if prev.sessionrange && curr.sessionrange then
prev.sessionrange:= prev.sessionrange + curr.sessionrange;
else
if prev notnull then
return next prev;
end if;
prev:= curr;
end if;
end loop;
return next prev;
end $$;
Results:
select *
from merge_ranges_in_test();
id | sessionrange | fk_user_id
----+-----------------------------------------------------+------------
1 | ["2016-01-14 17:57:01+01","2016-01-14 18:21:56+01"] | 1
5 | ["2016-01-15 00:18:08+01","2016-01-15 00:18:15+01"] | 1
7 | ["2016-01-15 00:18:16+01","2016-01-15 00:18:31+01"] | 1
6 | ["2016-01-15 00:38:12+01","2016-01-15 00:48:20+01"] | 1
4 | ["2016-01-15 00:18:00+01","2016-01-15 00:42:09+01"] | 2
9 | ["2016-01-15 00:18:12+01","2016-01-15 00:18:20+01"] | 3
10 | ["2016-01-15 01:32:12+01","2016-01-15 05:18:20+01"] | 3
11 | ["2016-01-15 00:18:16+01","2016-01-15 00:18:26+01"] | 4
(8 rows)
The problem is very interesting. I've tried to find a recursive solution but it seems the procedural attempt is most natural and efficient.
I have finally found a recursive solution. The query deletes overlapping rows and inserts their compacted equivalent:
with recursive cte (user_id, ids, range) as (
select t1.fk_user_id, array[t1.id, t2.id], t1.sessionrange + t2.sessionrange
from test t1
join test t2
on t1.fk_user_id = t2.fk_user_id
and t1.id < t2.id
and t1.sessionrange && t2.sessionrange
union all
select user_id, ids || t.id, range + sessionrange
from cte
join test t
on user_id = t.fk_user_id
and ids[cardinality(ids)] < t.id
and range && t.sessionrange
),
list as (
select distinct on(id) id, range, user_id
from cte, unnest(ids) id
order by id, upper(range)- lower(range) desc
),
deleted as (
delete from test
where id in (select id from list)
)
insert into test
select distinct on (range) id, range, user_id
from list
order by range, id;
Results:
select *
from test
order by 3, 2;
id | sessionrange | fk_user_id
----+-----------------------------------------------------+------------
1 | ["2016-01-14 17:57:01+01","2016-01-14 18:21:56+01"] | 1
5 | ["2016-01-15 00:18:08+01","2016-01-15 00:18:15+01"] | 1
7 | ["2016-01-15 00:18:16+01","2016-01-15 00:18:31+01"] | 1
6 | ["2016-01-15 00:38:12+01","2016-01-15 00:48:20+01"] | 1
4 | ["2016-01-15 00:18:00+01","2016-01-15 00:42:09+01"] | 2
9 | ["2016-01-15 00:18:12+01","2016-01-15 00:18:20+01"] | 3
10 | ["2016-01-15 01:32:12+01","2016-01-15 05:18:20+01"] | 3
11 | ["2016-01-15 00:18:16+01","2016-01-15 00:18:26+01"] | 4
(8 rows)
I need to calculate value of some column X based on some other columns of the current record and the value of X for the previous record (using some partition and order). Basically I need to implement query in the form
SELECT <some fields>,
<some expression using LAG(X) OVER(PARTITION BY ... ORDER BY ...) AS X
FROM <table>
This is not possible because only existing columns can be used in window function so I'm looking way how to overcome this.
Here is an example. I have a table with events. Each event has type and time_stamp.
create table event (id serial, type integer, time_stamp integer);
I wan't to find "duplicate" events (to skip them). By duplicate I mean the following. Let's order all events for given type by time_stamp ascending. Then
the first event is not a duplicate
all events that follow non duplicate and are within some time frame after it (that is their time_stamp is not greater then time_stamp of the previous non duplicate plus some constant TIMEFRAME) are duplicates
the next event which time_stamp is greater than previous non duplicate by more than TIMEFRAME is not duplicate
and so on
For this data
insert into event (type, time_stamp)
values
(1, 1), (1, 2), (2, 2), (1,3), (1, 10), (2,10),
(1,15), (1, 21), (2,13),
(1, 40);
and TIMEFRAME=10 result should be
time_stamp | type | duplicate
-----------------------------
1 | 1 | false
2 | 1 | true
3 | 1 | true
10 | 1 | true
15 | 1 | false
21 | 1 | true
40 | 1 | false
2 | 2 | false
10 | 2 | true
13 | 2 | false
I could calculate the value of duplicate field based on current time_stamp and time_stamp of the previous non-duplicate event like this:
WITH evt AS (
SELECT
time_stamp,
CASE WHEN
time_stamp - LAG(current_non_dupl_time_stamp) OVER w >= TIMEFRAME
THEN
time_stamp
ELSE
LAG(current_non_dupl_time_stamp) OVER w
END AS current_non_dupl_time_stamp
FROM event
WINDOW w AS (PARTITION BY type ORDER BY time_stamp ASC)
)
SELECT time_stamp, time_stamp != current_non_dupl_time_stamp AS duplicate
But this does not work because the field which is calculated cannot be referenced in LAG:
ERROR: column "current_non_dupl_time_stamp" does not exist.
So the question: can I rewrite this query to achieve the effect I need?
Naive recursive chain knitter:
-- temp view to avoid nested CTE
CREATE TEMP VIEW drag AS
SELECT e.type,e.time_stamp
, ROW_NUMBER() OVER www as rn -- number the records
, FIRST_VALUE(e.time_stamp) OVER www as fst -- the "group leader"
, EXISTS (SELECT * FROM event x
WHERE x.type = e.type
AND x.time_stamp < e.time_stamp) AS is_dup
FROM event e
WINDOW www AS (PARTITION BY type ORDER BY time_stamp)
;
WITH RECURSIVE ttt AS (
SELECT d0.*
FROM drag d0 WHERE d0.is_dup = False -- only the "group leaders"
UNION ALL
SELECT d1.type, d1.time_stamp, d1.rn
, CASE WHEN d1.time_stamp - ttt.fst > 20 THEN d1.time_stamp
ELSE ttt.fst END AS fst -- new "group leader"
, CASE WHEN d1.time_stamp - ttt.fst > 20 THEN False
ELSE True END AS is_dup
FROM drag d1
JOIN ttt ON d1.type = ttt.type AND d1.rn = ttt.rn+1
)
SELECT * FROM ttt
ORDER BY type, time_stamp
;
Results:
CREATE TABLE
INSERT 0 10
CREATE VIEW
type | time_stamp | rn | fst | is_dup
------+------------+----+-----+--------
1 | 1 | 1 | 1 | f
1 | 2 | 2 | 1 | t
1 | 3 | 3 | 1 | t
1 | 10 | 4 | 1 | t
1 | 15 | 5 | 1 | t
1 | 21 | 6 | 1 | t
1 | 40 | 7 | 40 | f
2 | 2 | 1 | 2 | f
2 | 10 | 2 | 2 | t
2 | 13 | 3 | 2 | t
(10 rows)
An alternative to a recursive approach is a custom aggregate. Once you master the technique of writing your own aggregates, creating transition and final functions is easy and logical.
State transition function:
create or replace function is_duplicate(st int[], time_stamp int, timeframe int)
returns int[] language plpgsql as $$
begin
if st is null or st[1] + timeframe <= time_stamp
then
st[1] := time_stamp;
end if;
st[2] := time_stamp;
return st;
end $$;
Final function:
create or replace function is_duplicate_final(st int[])
returns boolean language sql as $$
select st[1] <> st[2];
$$;
Aggregate:
create aggregate is_duplicate_agg(time_stamp int, timeframe int)
(
sfunc = is_duplicate,
stype = int[],
finalfunc = is_duplicate_final
);
Query:
select *, is_duplicate_agg(time_stamp, 10) over w
from event
window w as (partition by type order by time_stamp asc)
order by type, time_stamp;
id | type | time_stamp | is_duplicate_agg
----+------+------------+------------------
1 | 1 | 1 | f
2 | 1 | 2 | t
4 | 1 | 3 | t
5 | 1 | 10 | t
7 | 1 | 15 | f
8 | 1 | 21 | t
10 | 1 | 40 | f
3 | 2 | 2 | f
6 | 2 | 10 | t
9 | 2 | 13 | f
(10 rows)
Read in the documentation: 37.10. User-defined Aggregates and CREATE AGGREGATE.
This feels more like a recursive problem than windowing function. The following query obtained the desired results:
WITH RECURSIVE base(type, time_stamp) AS (
-- 3. base of recursive query
SELECT x.type, x.time_stamp, y.next_time_stamp
FROM
-- 1. start with the initial records of each type
( SELECT type, min(time_stamp) AS time_stamp
FROM event
GROUP BY type
) x
LEFT JOIN LATERAL
-- 2. for each of the initial records, find the next TIMEFRAME (10) in the future
( SELECT MIN(time_stamp) next_time_stamp
FROM event
WHERE type = x.type
AND time_stamp > (x.time_stamp + 10)
) y ON true
UNION ALL
-- 4. recursive join, same logic as base
SELECT e.type, e.time_stamp, z.next_time_stamp
FROM event e
JOIN base b ON (e.type = b.type AND e.time_stamp = b.next_time_stamp)
LEFT JOIN LATERAL
( SELECT MIN(time_stamp) next_time_stamp
FROM event
WHERE type = e.type
AND time_stamp > (e.time_stamp + 10)
) z ON true
)
-- The actual query:
-- 5a. All records from base are not duplicates
SELECT time_stamp, type, false
FROM base
UNION
-- 5b. All records from event that are not in base are duplicates
SELECT time_stamp, type, true
FROM event
WHERE (type, time_stamp) NOT IN (SELECT type, time_stamp FROM base)
ORDER BY type, time_stamp
There are a lot of caveats with this. It assumes no duplicate time_stamp for a given type. Really the joins should be based on a unique id rather than type and time_stamp. I didn't test this much, but it may at least suggest an approach.
This is my first time to try a LATERAL join. So there may be a way to simplify that moe. Really what I wanted to do was a recursive CTE with the recursive part using MIN(time_stamp) based on time_stamp > (x.time_stamp + 10), but aggregate functions are not allowed in CTEs in that manner. But it seems the lateral join can be used in the CTE.
I would like to know if there's a way to compute the sum of multiple columns in PostgreSQL.
I have a table with more than 80 columns and I have to write a query that adds each value from each column.
I tried with SUM(col1, col2, col3 etc) but it didn't work.
SELECT COALESCE(col1,0) + COALESCE(col2,0)
FROM yourtable
It depends on how you'd like to sum the values. If I read your question correctly, you are looking for the second SELECT from this example:
template1=# SELECT * FROM yourtable ;
a | b
---+---
1 | 2
4 | 5
(2 rows)
template1=# SELECT a + b FROM yourtable ;
?column?
----------
3
9
(2 rows)
template1=# SELECT SUM( a ), SUM( b ) FROM yourtable ;
sum | sum
-----+-----
5 | 7
(1 row)
template1=# SELECT SUM( a + b ) FROM yourtable ;
sum
-----
12
(1 row)
template1=#
Combined the current answers and used this to get total SUM:
SELECT SUM(COALESCE(col1,0) + COALESCE(col2,0)) FROM yourtable;
SELECT(
SELECT SUM(t.f)
FROM (VALUES (yourtable.col1), (yourtable.col2), (yourtable.col3)) t(f)
)
FROM yourtable;