Related
Given a table representing a many-many join between IDs like the following:
WITH t AS (
SELECT 1 AS id_1, 'a' AS id_2,
UNION ALL SELECT 2, 'a'
UNION ALL SELECT 2, 'b'
UNION ALL SELECT 3, 'b'
UNION ALL SELECT 4, 'c'
UNION ALL SELECT 5, 'c'
UNION ALL SELECT 6, 'd'
UNION ALL SELECT 6, 'e'
UNION ALL SELECT 7, 'f'
)
SELECT * FROM t
id_1
id_2
1
a
2
a
2
b
3
b
4
c
5
c
6
d
6
e
7
f
I would like to be able recursively join then aggregate rows in order to find each disconnected sub-graph represented by these links - that is each collection of IDs that are linked together:
The desired output for the example above would look something like this:
id_1_coll
id_2_coll
1, 2, 3
a, b
4, 5
c
6
d, e
7
f
where each row contains all the other IDs one could reach following the links in the table.
Note that 1 links to b even although there is no explicit link row because we can follow the path 1 --> a --> 2 --> b using the links in the first 3 rows.
One potential approach is to remodel the relationships between id_1 and id_2 such that we get all the links from id_1 to itself then use a recursive common table expression to traverse all the possible paths between id_1 values then aggregate (somewhat arbitrarily) to the lowest such value that can be reached from each id_1.
Explanation
Our steps are
Remodel the relationship into a series of self-joins for id_1
Map each id_1 to the lowest id_1 that it is linked to via a recursive CTE
Aggregate the recursive CTE using the lowest id_1s as the GROUP BY column and grabbing all the linked id_1 and id_2 values via the ARRAY_AGG() function
We can use something like this to remodel the relationships into a self join (1.):
SELECT
a.id_1, a.id_2, b.id_1 AS linked_id
FROM t as a
INNER JOIN t as b
ON a.id_2 = b.id_2
WHERE a.id_1 != b.id_1
Next - to set up the recursive table expression (2.) we can tweak the query above to also give us the lowest (LEAST) of the values for id_1 at each link then use this as the base iteration:
WITH RECURSIVE base_iter AS (
SELECT
a.id_1, b.id_1 AS linked_id, LEAST(a.id_1, b.id_1) AS lowest_linked_id
FROM t as a
INNER JOIN t as b
ON a.id_2 = b.id_2
WHERE a.id_1 != b.id_1
)
We can also grab the lowest id_1 value at this time:
id_1
linked_id
lowest_linked_id
1
2
1
2
1
1
2
3
2
3
2
2
4
5
4
5
4
4
For our recursive loop, we want to maintain an ARRAY of linked ids and join each new iteration such that the id_1 value of the n+1th iteration is equal to the linked_id value of the nth iteration AND the nth linked_id value is not in the array of previously linked ids.
We can code this as follows:
recursive_loop AS (
SELECT id_1, linked_id, lowest_linked_id, [linked_id ] AS linked_ids
FROM base_iter
UNION ALL
SELECT
prev_iter.id_1, prev_iter.linked_id,
iter.lowest_linked_id,
ARRAY_CONCAT(iter.linked_ids, [prev_iter.linked_id])
FROM base_iter AS prev_iter
JOIN recursive_loop AS iter
ON iter.id_1 = prev_iter.linked_id
AND iter.lowest_linked_id < prev_iter.lowest_linked_id
AND prev_iter.linked_id NOT IN UNNEST(iter.linked_ids )
)
Giving us the following results:
|id_1|linked_id|lowest_linked_id|linked_ids|
|----|---------|------------|---|
|3|2|1|[1,2]|
|2|3|1|[1,2,3]|
|4|5|4|[5]|
|1|2|1|[2]|
|5|4|4|[4]|
|2|3|2|[3]|
|2|1|1|[1]|
|3|2|2|[2]|
which we can now link back to the original table for the id_2 values then aggregate (3.) as shown in the complete query below
Solution
WITH RECURSIVE t AS (
SELECT 1 AS id_1, 'a' AS id_2,
UNION ALL SELECT 2, 'a'
UNION ALL SELECT 2, 'b'
UNION ALL SELECT 3, 'b'
UNION ALL SELECT 4, 'c'
UNION ALL SELECT 5, 'c'
UNION ALL SELECT 6, 'd'
UNION ALL SELECT 6, 'e'
UNION ALL SELECT 7, 'f'
),
base_iter AS (
SELECT
a.id_1, b.id_1 AS linked_id, LEAST(a.id_1, b.id_1) AS lowest_linked_id
FROM t as a
INNER JOIN t as b
ON a.id_2 = b.id_2
WHERE a.id_1 != b.id_1
),
recursive_loop AS (
SELECT id_1, linked_id, lowest_linked_id, [linked_id ] AS linked_ids
FROM base_iter
UNION ALL
SELECT
prev_iter.id_1, prev_iter.linked_id,
iter.lowest_linked_id,
ARRAY_CONCAT(iter.linked_ids, [prev_iter.linked_id])
FROM base_iter AS prev_iter
JOIN recursive_loop AS iter
ON iter.id_1 = prev_iter.linked_id
AND iter.lowest_linked_id < prev_iter.lowest_linked_id
AND prev_iter.linked_id NOT IN UNNEST(iter.linked_ids )
),
link_back AS (
SELECT
t.id_1, IFNULL(lowest_linked_id, t.id_1) AS lowest_linked_id, t.id_2
FROM t
LEFT JOIN recursive_loop
ON t.id_1 = recursive_loop.id_1
),
by_id_1 AS (
SELECT
id_1,
MIN(lowest_linked_id) AS grp
FROM link_back
GROUP BY 1
),
by_id_2 AS (
SELECT
id_2,
MIN(lowest_linked_id) AS grp
FROM link_back
GROUP BY 1
),
result AS (
SELECT
by_id_1.grp,
ARRAY_AGG(DISTINCT id_1 ORDER BY id_1) AS id1_coll,
ARRAY_AGG(DISTINCT id_2 ORDER BY id_2) AS id2_coll,
FROM
by_id_1
INNER JOIN by_id_2
ON by_id_1.grp = by_id_2.grp
GROUP BY grp
)
SELECT grp, TO_JSON(id1_coll) AS id1_coll, TO_JSON(id2_coll) AS id2_coll
FROM result ORDER BY grp
Giving us the required output:
grp
id1_coll
id2_coll
1
[1,2,3]
[a,b]
4
[4,5]
[c]
6
[6]
[d,e]
7
[7]
[f]
Limitations/Issues
Unfortunately this approach is inneficient (we have to traverse every single pathway before aggregating it back together) and fails with the real-world case where we have several million join rows. When trying to execute on this data BigQuery runs up a huge "Slot time consumed" then eventually errors out with:
Resources exceeded during query execution: Your project or organization exceeded the maximum disk and memory limit available for shuffle operations. Consider provisioning more slots, reducing query concurrency, or using more efficient logic in this job.
I hope there might be a better way of doing the recursive join such that pathways can be merged/aggregated as we go (if we have an id_1 value AND a linked_id in already in the list of linked_ids we dont need to check it further).
Using ROW_NUMBER() the query is as the follow:
WITH RECURSIVE
t AS (
SELECT 1 AS id_1, 'a' AS id_2,
UNION ALL SELECT 2, 'a'
UNION ALL SELECT 2, 'b'
UNION ALL SELECT 3, 'b'
UNION ALL SELECT 4, 'c'
UNION ALL SELECT 5, 'c'
UNION ALL SELECT 6, 'd'
UNION ALL SELECT 6, 'e'
UNION ALL SELECT 7, 'f'
),
t1 AS (
SELECT ROW_NUMBER() OVER(ORDER BY t.id_1) n, t.id_1, t.id_2 FROM t
),
t2 AS (
SELECT n, [n] n_arr, [id_1] arr_1, [id_2] arr_2, id_1, id_2 FROM t1
WHERE n IN (SELECT MIN(n) FROM t1 GROUP BY id_1)
UNION ALL
SELECT t2.n, ARRAY_CONCAT(t2.n_arr, [t1.n]),
CASE WHEN t1.id_1 NOT IN UNNEST(t2.arr_1)
THEN ARRAY_CONCAT(t2.arr_1, [t1.id_1])
ELSE t2.arr_1 END,
CASE WHEN t1.id_2 NOT IN UNNEST(t2.arr_2)
THEN ARRAY_CONCAT(t2.arr_2, [t1.id_2])
ELSE t2.arr_2 END,
t1.id_1, t1.id_2
FROM t2 JOIN t1 ON
t2.n < t1.n AND
t1.n NOT IN UNNEST(t2.n_arr) AND
(t2.id_1 = t1.id_1 OR t2.id_2 = t1.id_2) AND
(t1.id_1 NOT IN UNNEST(t2.arr_1) OR t1.id_2 NOT IN UNNEST(t2.arr_2))
),
t3 AS (
SELECT
n,
ARRAY_AGG(DISTINCT id_1 ORDER BY id_1) arr_1,
ARRAY_AGG(DISTINCT id_2 ORDER BY id_2) arr_2
FROM t2
WHERE n IN (SELECT MIN(n) FROM t2 GROUP BY id_1)
GROUP BY n
)
SELECT n, TO_JSON(arr_1), TO_JSON(arr_2) FROM t3 ORDER BY n
t1 : Append with row numbers.
t2 : Extract rows matching either id_1 or id_2 by recursive query.
t3 : Make arrays from id_1 and id_2 with ARRAY_AGG().
However, it may not help your Limitations/Issues.
The way this question is phrased makes it appear you want "show me distinct groups from a presorted list, unchained to a previous group". For that, something like this should suffice (assuming auto-incrementing order/one or both id's move to the next value):
SELECT GrpNr,
STRING_AGG(DISTINCT CAST(id_1 as STRING), ',') as id_1_coll,
STRING_AGG(DISTINCT CAST(id_2 as STRING), ',') as id_2_coll
FROM
(
SELECT id_1, id_2,
SUM(CASE WHEN a.id_1 <> a.previous_id_1 and a.id_2 <> a.previous_id_2 THEN 1 ELSE 0 END)
OVER (ORDER BY RowNr) as GrpNr
FROM
(
SELECT *,
ROW_NUMBER() OVER () as RowNr,
LAG(t.id_1, 1) OVER (ORDER BY 1) AS previous_id_1,
LAG(t.id_2, 1) OVER (ORDER BY 1) AS previous_id_2
FROM t
) a
ORDER BY RowNr
) a
GROUP BY GrpNr
ORDER BY GrpNr
I don't think this is the question you mean to ask. This seems to be a graph-walking problem as referenced in the other answers, and in the response from #GordonLinoff to the question here, which I tested (and presume works for BigQuery).
This can also be done using sequential updates as done by #RomanPekar
here (which I also tested). The main consideration seems to be performance. I'd assume dbms have gotten better at recursion since this was posted.
Rolling it up in either case should be fairly easy using String_Agg() as given above or as you have.
I'd be curious to see a more accurate representation of the data. If there is some consistency to how the data is stored/limitations to levels of nesting/other group structures there may be a shortcut approach other than recursion or iterative updates.
Assume there is a table called "allvalues" with a column named "column".
This column contains the values "A" to "J" while missing the "H".
I am given a set of values from "G" to "J".
How can I query the table to see which value of my set is missing in the column?
The following does not work:
select * from allvalues where column not in ('G', 'H', 'I', 'J')
This query would result in A, B, C, D, E, F, H which also contains values not included in the given set.
Obviously in such a small data pool the missing value is noticeable by eye, but imagine more entries in the table and a bigger set.
You need to start with a (derived) table with the values you are checking. One explicit method is:
with testvalues as (
select 'G' as val from dual union all
select 'H' as val from dual union all
select 'I' as val from dual union all
select 'J' as val from dual
)
select tv.val
from testvalues tv
where not exists (select 1 from allvalues av where av.column = tv.val);
Often, the values originate through a query or a table. So explicitly declaring them is unnecessary -- you can replace that part with a subquery.
Depends on which SQL syntax you can use, but basically you want to check your table allvalues + the extra values.
eg:
SELECT *
FROM ALLVALUES
WHERE COLUMN NOT IN (
( select s.column from allvalues s )
and column not in ('G', 'H', 'I', 'J')
this will work:
select * from table1;
G
H
I
J
select * from table1
minus
(select * from table1
intersect
select column from allvalues
)
sample input:
select * from ns_table10;
G
H
I
J
SELECT * FROM ns_table11;
A
B
C
D
E
F
G
J
I
select * from ns_table10
minus
(select * from ns_table10
intersect
select * from ns_table11
);
output:
H
For Example,
select A,B,C,D,E,YEAR
FROM t1
where t1.year = 2018
UNION ALL
select A,B,C,D,E,YEAR
FROM t2
where t2.year = 2017
execute like this
A --- B----C----D----E----YEAR
2 --- 4----6----8----10---2018
1 --- 3----5----7----9----2017
I would like to have a result like this
2018 2017
A 2 1
B 4 3
C 6 5
D 8 7
E 10 9
I know I should use pivot, and googled around, but I can not figure out how to write a code to have a result like above.
Thanks
Assuming you are using Oracle 11.1 or above, you can use the pivot and unpivot operators. In your problem, the data is already "pivoted" one way, but you want it pivoted the other way; so you must un-pivot first, and then re-pivot the way you want it. In the solution below, the data is read from the table (I use a WITH clause to generate the test data, but you don't need the WITH clause, you can start at SELECT and use your actual table and column names). The data is fed through unpivot and then immediately to pivot - you don't need subqueries or anything like that.
Note about column names: don't use year, it is an Oracle keyword and you will cause confusion if not (much) worse. And in the output, you can't have 2018 and such as column names - identifiers must begin with a letter. You can go around these limitations using names in double quotes; that is a very poor practice though, best left just to the Oracle parser and not used by us humans. You will see I called the input column yr and the output columns y2018 and such.
with
inputs ( a, b, c, d, e, yr ) as (
select 2, 4, 6, 8, 10, 2018 from dual union all
select 1, 3, 5, 7, 9, 2017 from dual
)
select col, y2018, y2017
from inputs
unpivot ( val for col in (a as 'A', b as 'B', c as 'C', d as 'D', e as 'E') )
pivot ( min(val) for yr in (2018 as y2018, 2017 as y2017) )
order by col -- if needed
;
COL Y2018 Y2017
--- ---------- ----------
A 2 1
B 4 3
C 6 5
D 8 7
E 10 9
ADDED:
Here is how this used to be done (before the pivot and unpivot were introduced in Oracle 11.1). Unpivoting was done with a cross join to a small helper table, with a single column and as many rows as there were columns to unpivot in the base table - in this case, five columns, a, b, c, d, e need to be unpivoted, so the helper table has five rows. And pivoting was done with conditional aggregation. Both can be combined into a single query - there is no need for subqueries (other than to create the helper "table" or inline view).
Note, importantly, that the base table is read just once. Other methods of unpivoting are much more inefficient, because they require reading the base table multiple times.
select decode(lvl, 1, 'A', 2, 'B', 3, 'C', 4, 'D', 5, 'E') as col,
max(case yr when 2018 then decode(lvl, 1, a, 2, b, 3, c, 4, d, 5, e) end) as y2018,
max(case yr when 2017 then decode(lvl, 1, a, 2, b, 3, c, 4, d, 5, e) end) as y2017
from inputs cross join ( select level as lvl from dual connect by level <= 5 )
group by decode(lvl, 1, 'A', 2, 'B', 3, 'C', 4, 'D', 5, 'E')
order by decode(lvl, 1, 'A', 2, 'B', 3, 'C', 4, 'D', 5, 'E')
;
This looks worse than it is; the same decode() function is called three times, but with exactly the same arguments, so it is calculated only once, the value is cached and it is reused in the other places. (It is calculated for group by and then reused for select and for order by.)
To test, you can use the same WITH clause as above - or your actual data.
decode() is proprietary to Oracle, but the same can be written with case expressions (essentially identical to the decode() approach, just different syntax) and it will work in most other database products.
This is a bit tricky -- unpivotting and repivotting. Here is one way:
select col,
max(case when year = 2018 then val end) as val_2018,
max(case when year = 2017 then val end) as val_2017
from ((select 'A' as col, A as val, YEAR from t1 where year = 2018) union all
(select 'B' as col, B as val, YEAR from t1 where year = 2018) union all
(select 'C' as col, C as val, YEAR from t1 where year = 2018) union all
(select 'D' as col, D as val, YEAR from t1 where year = 2018) union all
(select 'E' as col, D as val, YEAR from t1 where year = 2018) union all
(select 'A' as col, A as val, YEAR from t2 where year = 2017) union all
(select 'B' as col, B as val, YEAR from t2 where year = 2017) union all
(select 'C' as col, C as val, YEAR from t2 where year = 2017) union all
(select 'D' as col, D as val, YEAR from t2 where year = 2017) union all
(select 'E' as col, D as val, YEAR from t2 where year = 2017)
) tt
group by col;
You don't specify the database, but this is pretty database independent.
Suppose I have a list of values, such as 1, 2, 3, 4, 5 and a table where some of those values exist in some column. Here is an example:
id name
1 Alice
3 Cindy
5 Elmore
6 Felix
I want to create a SELECT statement that will include all of the values from my list as well as the information from those rows that match the values, i.e., perform a LEFT OUTER JOIN between my list and the table, so the result would be like follows:
id name
1 Alice
2 (null)
3 Cindy
4 (null)
5 Elmore
How do I do that without creating a temp table or using multiple UNION operators?
If in Microsoft SQL Server 2008 or later, then you can use Table Value Constructor
Select v.valueId, m.name
From (values (1), (2), (3), (4), (5)) v(valueId)
left Join otherTable m
on m.id = v.valueId
Postgres also has this construction VALUES Lists:
SELECT * FROM (VALUES (1, 'one'), (2, 'two'), (3, 'three')) AS t (num,letter)
Also note the possible Common Table Expression syntax which can be handy to make joins:
WITH my_values(num, str) AS (
VALUES (1, 'one'), (2, 'two'), (3, 'three')
)
SELECT num, txt FROM my_values
With Oracle it's possible, though heavier From ASK TOM:
with id_list as (
select 10 id from dual union all
select 20 id from dual union all
select 25 id from dual union all
select 70 id from dual union all
select 90 id from dual
)
select * from id_list;
the following solution for oracle is adopted from this source. the basic idea is to exploit oracle's hierarchical queries. you have to specify a maximum length of the list (100 in the sample query below).
select d.lstid
, t.name
from (
select substr(
csv
, instr(csv,',',1,lev) + 1
, instr(csv,',',1,lev+1 )-instr(csv,',',1,lev)-1
) lstid
from (select ','||'1,2,3,4,5'||',' csv from dual)
, (select level lev from dual connect by level <= 100)
where lev <= length(csv)-length(replace(csv,','))-1
) d
left join test t on ( d.lstid = t.id )
;
check out this sql fiddle to see it work.
Bit late on this, but for Oracle you could do something like this to get a table of values:
SELECT rownum + 5 /*start*/ - 1 as myval
FROM dual
CONNECT BY LEVEL <= 100 /*end*/ - 5 /*start*/ + 1
... And then join that to your table:
SELECT *
FROM
(SELECT rownum + 1 /*start*/ - 1 myval
FROM dual
CONNECT BY LEVEL <= 5 /*end*/ - 1 /*start*/ + 1) mypseudotable
left outer join myothertable
on mypseudotable.myval = myothertable.correspondingval
Assuming myTable is the name of your table, following code should work.
;with x as
(
select top (select max(id) from [myTable]) number from [master]..spt_values
),
y as
(select row_number() over (order by x.number) as id
from x)
select y.id, t.name
from y left join myTable as t
on y.id = t.id;
Caution: This is SQL Server implementation.
fiddle
For getting sequential numbers as required for part of output (This method eliminates values to type for n numbers):
declare #site as int
set #site = 1
while #site<=200
begin
insert into ##table
values (#site)
set #site=#site+1
end
Final output[post above step]:
select * from ##table
select v.id,m.name from ##table as v
left outer join [source_table] m
on m.id=v.id
Suppose your table that has values 1,2,3,4,5 is named list_of_values, and suppose the table that contain some values but has the name column as some_values, you can do:
SELECT B.id,A.name
FROM [list_of_values] AS B
LEFT JOIN [some_values] AS A
ON B.ID = A.ID
I have data like this in a table
NAME PRICE
A 2
B 3
C 5
D 9
E 5
I want to display all the values in one row; for instance:
A,2|B,3|C,5|D,9|E,5|
How would I go about making a query that will give me a string like this in Oracle? I don't need it to be programmed into something; I just want a way to get that line to appear in the results so I can copy it over and paste it in a word document.
My Oracle version is 10.2.0.5.
-- Oracle 10g --
SELECT deptno, WM_CONCAT(ename) AS employees
FROM scott.emp
GROUP BY deptno;
Output:
10 CLARK,MILLER,KING
20 SMITH,FORD,ADAMS,SCOTT,JONES
30 ALLEN,JAMES,TURNER,BLAKE,MARTIN,WARD
I know this is a little late but try this:
SELECT LISTAGG(CONCAT(CONCAT(NAME,','),PRICE),'|') WITHIN GROUP (ORDER BY NAME) AS CONCATDATA
FROM your_table
Usually when I need something like that quickly and I want to stay on SQL without using PL/SQL, I use something similar to the hack below:
select sys_connect_by_path(col, ', ') as concat
from
(
select 'E' as col, 1 as seq from dual
union
select 'F', 2 from dual
union
select 'G', 3 from dual
)
where seq = 3
start with seq = 1
connect by prior seq+1 = seq
It's a hierarchical query which uses the "sys_connect_by_path" special function, which is designed to get the "path" from a parent to a child.
What we are doing is simulating that the record with seq=1 is the parent of the record with seq=2 and so fourth, and then getting the full path of the last child (in this case, record with seq = 3), which will effectively be a concatenation of all the "col" columns
Adapted to your case:
select sys_connect_by_path(to_clob(col), '|') as concat
from
(
select name || ',' || price as col, rownum as seq, max(rownum) over (partition by 1) as max_seq
from
(
/* Simulating your table */
select 'A' as name, 2 as price from dual
union
select 'B' as name, 3 as price from dual
union
select 'C' as name, 5 as price from dual
union
select 'D' as name, 9 as price from dual
union
select 'E' as name, 5 as price from dual
)
)
where seq = max_seq
start with seq = 1
connect by prior seq+1 = seq
Result is: |A,2|B,3|C,5|D,9|E,5
As you're in Oracle 10g you can't use the excellent listagg(). However, there are numerous other string aggregation techniques.
There's no particular need for all the complicated stuff. Assuming the following table
create table a ( NAME varchar2(1), PRICE number);
insert all
into a values ('A', 2)
into a values ('B', 3)
into a values ('C', 5)
into a values ('D', 9)
into a values ('E', 5)
select * from dual
The unsupported function wm_concat should be sufficient:
select replace(replace(wm_concat (name || '#' || price), ',', '|'), '#', ',')
from a;
REPLACE(REPLACE(WM_CONCAT(NAME||'#'||PRICE),',','|'),'#',',')
--------------------------------------------------------------------------------
A,2|B,3|C,5|D,9|E,5
But, you could also alter Tom Kyte's stragg, also in the above link, to do it without the replace functions.
Here is another approach, using model clause:
-- sample of data from your question
with t1(NAME1, PRICE) as(
select 'A', 2 from dual union all
select 'B', 3 from dual union all
select 'C', 5 from dual union all
select 'D', 9 from dual union all
select 'E', 5 from dual
) -- the query
select Res
from (select name1
, price
, rn
, res
from t1
model
dimension by (row_number() over(order by name1) rn)
measures (name1, price, cast(null as varchar2(101)) as res)
(res[rn] order by rn desc = name1[cv()] || ',' || price[cv()] || '|' || res[cv() + 1])
)
where rn = 1
Result:
RES
----------------------
A,2|B,3|C,5|D,9|E,5|
SQLFiddle Example
Something like the following, which is grossly inefficient and untested.
create function foo returning varchar2 as
(
declare bar varchar2(8000) --arbitrary number
CURSOR cur IS
SELECT name,price
from my_table
LOOP
FETCH cur INTO r;
EXIT WHEN cur%NOTFOUND;
bar:= r.name|| ',' ||r.price || '|'
END LOOP;
dbms_output.put_line(bar);
return bar
)
Managed to get till here using xmlagg: using oracle 11G from sql fiddle.
Data Table:
COL1 COL2 COL3
1 0 0
1 1 1
2 0 0
3 0 0
3 1 0
SELECT
RTRIM(REPLACE(REPLACE(
XMLAgg(XMLElement("x", col1,',', col2, col3)
ORDER BY col1), '<x>'), '</x>', '|')) AS COLS
FROM ab
;
Results:
COLS
1,00| 3,00| 2,00| 1,11| 3,10|
* SQLFIDDLE DEMO
Reference to read on XMLAGG