How can GROUP BY based on the union of two columns be achieved performantly? There may be NULL values in either column. Something like (obviously this doesn't work):
SELECT a.val, b.val
FROM a
LEFT JOIN b on a.id = b.id
GROUP BY UNION(a.val, b.val)
With results like:
a.val | b.val
-----------
1 1
2 2
NULL 3
4 NULL
5 5
Thanks!
Why can't you use NVL
SELECT NVL(a.val, b.val) FROM a LEFT JOIN b on a.id = b.id
GROUP BY NVL(a.val, b.val)
Related
I have 3 tables:
Basic
id
name
description
2
Name1
description2
3
Name2
description3
LinkA
id
linkA_ID
2
344
3
3221
2
6642
3
2312
2
323
LinkB
id
linkB_ID
2
8287
3
42466
2
616422
3
531
2
2555
2
8592
3
1122
2
33345
I want to get results as the table below:
id
name
description
linkA_count
linkB_count
2
Name1
description2
3
2
3
Name2
description3
5
3
my query:
SELECT
a.id
,a.name
,a.description
,COUNT(b.linkA_ID) AS linkA_count
,COUNT(c.linkB_ID) AS linkb_count
FROM
basic a
JOIN linkA b on (a.id = b.id)
JOIN linkb c on (a.id = c.id)
GROUP BY
a.id
,a.name
,a.description
Result from the query is count of linkA always same as linkB
A more traditional approach is to use "derived tables" (subqueries) so that the counts are performed before joins multiply the rows. Using left joins allows for all id's in basic to be returned by the query even if there are no related rows in either joined tables.
select
basic.id
, coalesce(a.LinkACount,0) LinkACount
, coalesce(b.linkBCount,0) linkBCount
from basic
left join (
select id, Count(linkA_ID) LinkACount from LinkA group by id
) as a on a.id=basic.id
left join (
select id, Count(linkB_ID) LinkBCount from LinkB group by id
) as b on b.id=basic.id
Try This (using SubQuery)
SELECT
basic.id
,basic.name
,basic.description
,(select Count(linkA_ID) from LinkA where LinkA.id=basic.id) as LinkACount
,(select Count(linkB_ID) from LinkB where LinkB.id=basic.id) as LinkBCount FROM basic
Method 2 (Try CTE)
with a as(select id,Count(linkA_ID)LinkACount from LinkA group by id)
, b as (select id,Count(linkB_ID)LinkBCount from LinkB group by id)
select basic.id,a.LinkACount,b.linkBCount
from basic
join a on (a.id=basic.id)
join b on (b.id=basic.id)
If you only select from your table you see why your query cannot work.
SELECT
*
FROM
basic a
JOIN linkA b on (a.id = b.id)
JOIN linkb c on (a.id = c.id)
WHERE a.ID = 3
=> just use distinct in your count
SELECT
a.id
,a.name
,a.description
,COUNT(DISTINCT(b.linkA_ID)) AS linkA_count
,COUNT(DISTINCT(c.linkB_ID)) AS linkb_count
FROM
basic a
JOIN linkA b on (a.id = b.id)
JOIN linkb c on (a.id = c.id)
GROUP BY
a.id
,a.name
,a.description
I have two datasets in Oracle Table1 and Table2.
When I run this:
SELECT A.ID, B.NUM_X
FROM TABLE1 A
LEFT JOIN TABLE2 B ON A.ID=B.ID
WHERE B.BOOK = 1
It returns this.
ID NUM_X
1 10
1 5
1 9
2 2
2 1
3 20
3 11
What I want are the DISTINCT ID where NUM_X is the MAX value, something like this:
ID NUM_x
1 10
2 2
3 20
You can use aggregation:
SELECT A.ID, MAX(B.NUM_X)
FROM TABLE1 A LEFT JOIN
TABLE2 B
ON A.ID = B.ID
WHERE B.BOOK = 1
GROUP BY A.ID;
If you wanted additional columns, I would recommend window functions:
SELECT A.ID, MAX(B.NUM_X)
FROM TABLE1 A LEFT JOIN
(SELECT B.*,
ROW_NUMBER() OVER (PARTITION BY ID ORDER BY NUM_X DESC) as seqnum
FROM TABLE2 B
) B
ON A.ID = B.ID AND B.seqnum = 1
WHERE B.BOOK = 1
GROUP BY A.ID;
I have 3 tables. The main one in which I want to retrieve some information and two others for row count only.
I used a request like this :
SELECT A.*,
COUNT(B.id) AS b_count
FROM A
LEFT JOIN B on B.a_id = A.id
WHERE A.id > 50 AND B.ID < 100
GROUP BY A.id
from Gerry Shaw's comment here. It works perfectly but only for one table.
Now I need to add the row count for the third (C) table. I tried
SELECT A.*,
COUNT(B.id) AS b_count
COUNT(C.id) AS c_count
FROM A
LEFT JOIN B on B.a_id = A.id
LEFT JOIN C on C.a_id = A.id
GROUP BY A.id
but, because of the two left joins, my b_count and my c_count are false and equal to each other. In fact my actual b_count and c_count are equal to real_b_count*real_c_count. Any idea of how I could fix this without adding a lot of complexity/subqueries ?
Data sample as requested:
Table A (primary key : id)
id | data1 | data2
------+-------+-------
1 | 0,45 | 0,79
----------------------
2 | -2,24 | -0,25
----------------------
3 | 1,69 | 1,23
Table B (primary key : (a_id,fruit))
a_id | fruit
------+-------
1 | apple
------+-------
1 | banana
--------------
2 | apple
Table C (primary key : (a_id,color))
a_id | color
------+-------
2 | blue
------+-------
2 | purple
--------------
3 | blue
expected result:
id | data1 | data2 | b_count | c_count
------+-------+-------+---------+--------
1 | 0,45 | 0,79 | 2 | 0
----------------------+---------+--------
2 | -2,24 | -0,25 | 1 | 2
----------------------+---------+--------
3 | 1,69 | 1,23 | 0 | 1
There are two possible solutions. One is using subqueries behind SELECT
SELECT A.*,
(
SELECT COUNT(B.id) FROM B WHERE B.a_id = A.id AND B.ID < 100
) AS b_count,
(
SELECT COUNT(C.id) FROM C WHERE C.a_id = A.id
) AS c_count
FROM A
WHERE A.id > 50
the second are two SQL queries joined together
SELECT t1.*, t2.c_count
FROM
(
SELECT A.*,
COUNT(B.id) AS b_count
FROM A
LEFT JOIN B on B.a_id = A.id
WHERE A.id > 50 AND B.ID < 100
GROUP BY A.id
) t1
JOIN
(
SELECT A.*,
COUNT(C.id) AS c_count
FROM A
LEFT JOIN C on C.a_id = A.id
WHERE A.id > 50
GROUP BY A.id
) t2 ON t1.id = t2.id
I prefer the second syntax since it clearly shows the optimizer that you are interested in GROUP BY, however, the query plans are usually the same.
If tables B & C also have their own key fields, then you can use COUNT DISTINCT on the primary key rather than foreign key. That gets around the multi-line problem you see on link to several tables. If you can post the table structures then we can advise further.
Try something like this
SELECT A.*,
(SELECT COUNT(B.id) FROM B WHERE B.a_id = A.id) AS b_count,
(SELECT COUNT(C.id) FROM C WHERE C.a_id = A.id) AS c_count
FROM A
That is the easier way I can think:
Create table #a (id int, data1 float, data2 float)
Create table #b (id int, fruit varchar(50))
Create table #c (id int, color varchar(50))
Insert into #a
SELECT 1, 0.45, 0.79
UNION ALL SELECT 2, -2.24, -0.25
UNION ALL SELECT 3, 1.69, 1.23
Insert into #b
SELECT 1, 'apple'
UNION ALL SELECT 1, 'banana'
UNION ALL SELECT 2, 'orange'
Insert into #c
SELECT 2, 'blue'
UNION ALL SELECT 2, 'purple'
UNION ALL SELECT 3, 'orange'
SELECT #a.*,
(SELECT COUNT(#b.id) FROM #b where #b.id = #a.id) AS b_count,
(SELECT COUNT(#c.id) FROM #c where #c.id = #a.id) AS b_count
FROM #a
ORDER BY #a.id
Result:
id data1 data2 b_count b_count
1 0,45 0,79 2 0
2 -2,24 -0,25 1 2
3 1,69 1,23 0 1
If table b and c have unique id, you can try this:
SELECT A.*,
COUNT(distinct B.fruit) AS b_count,
COUNT(distinct C.color) AS c_count
FROM A
LEFT JOIN B on B.a_id = A.id
LEFT JOIN C on C.a_id = A.id
GROUP BY A.id
See SQLFiddle MySQL demo.
I have two table
table A
name id
ABC 1
PQR 2
XYZ 1
QWE 2
DFG 3
Another table
table B
id idname
1 stuart
2 bob
3 alex
expected output
id idname count
1 stuart 2
2 bob 2
3 alex 1
Iam using oracle 9i, Is it possible to obtain the expected result?
I have tried using distinct keyword but its not helping as it provides only the total count
That's simple. Join and count:
select b.id,
b.idname,
count(*) as cnt
from table_a a
join table_b b on a.id = b.id
group by b.id, b.idname;
If you need all the record from table b even if there is no corresponding row in table a, you can use an outer join:
select b.id,
b.idname,
count(a.id) as cnt
from table_a a
right join table_b b on a.id = b.id
group by b.id, b.idname;
Same can be achieved by using a left join:
select b.id,
b.idname,
count(a.id) as cnt
from table_b b
left join table_a a on a.id = b.id
group by b.id, b.idname;
Use JOIN to get data from both tables and use the aggregate function COUNT with GROUP BY.
Query
select t1.id, t1.idname, count(t2.name) as count
from TableB t1
left join TableA t2
on t1.id = t2.id
group by t1.id, t1.idname
order by count(t2.name) desc, t1.id;;
How can i join the below tables
TableA TableB TableC TableD
ID ID_C ID ID_A Value ID ID ID_C Value
1 1 1 1 a 1 1 1 a
2 1 b 2 1 b
in order to get the Result like
Result
ID ID_B Value ID_C ID_D Value
1 1 a 1 1 a
1 2 b 1 2 b
and my result shouldn't contain 1 2 b 1 1 b and both value columns cannot always have same values so it cannot be used in a condition.
To make it simplier,
Resultant Table TableA TableB
ID Value ID Value ID ID_A
1 a 1 a 1 1
1 b 2 g 2 1
2 a 3 d 3 2
3 c 4 3
Now i need to join the Resultant Table with TableA,TableB inorder to get some of the columns from TableA,TableB and ResultantTable.ID=TableA.ID and TableB.ID_A=TableA.ID since its a foreign key.
Doing the Join with TableB turns to duplicates. Since ID=1 occurs twice i get 4 records where ID=1, when there are only 2 records. It can be done with distinct or group by but i need other columns as well to be displayed.How do i do both in the process.
SELECT A.ID, B.ID, B.Value, C.ID, D.ID, D.Value
FROM TableA A
INNER JOIN TableB B ON A.ID = B.ID_A
INNER JOIN TableC C ON A.ID_C = C.ID
INNER JOIN TableD D ON B.ID = D.ID AND C.ID = D.ID_C
You tell us that the field "value" in TableB should not be different from the field "value" in TableD? Could we replace the B.ID = D.ID with B.Value = D.Value so solve your problem?
Are you sure, that is the way that is suppose to work?
Try:
SELECT A.ID, B.ID ID_B, B.Value Value_B, C.ID ID_C, D.ID ID_D, D.Value Value_D
FROM TableA A
JOIN TableB B ON A.ID = B.ID_A
JOIN TableC C ON A.ID_C = C.ID
JOIN TableD D ON B.Value = D.Value AND C.ID = D.ID_C