How to update a table based on count which is derived by group by on two attributes?
Eg:
Thers a table having columns a,b,c
I need to update c based on count which has common(a,b)
UPDATE in PostgreSQL has a FROM extension you could use:
update YourTable as yt1
set c = case when aggr.cnt > 5 then 'Q' else 'Z' end
from (
select a
, b
, count(*) as cnt
from YourTable
group by
a
, b
) as aggr
where aggr.a = yt1.a
and aggr.b = yt1.b
Related
Consider following table:
Number | Value
1 a
1 b
1 a
2 a
2 a
3 c
4 a
5 d
5 a
I want to choose every row, where the value for one number is the same, so my result should be:
Number | Value
2 a
3 c
4 a
I manage to get the right numbers by using nested
SQL-Statements like below. I am wondering if there is a simpler solution for my problem.
SELECT
a.n,
COUNT(n)
FROM
(
SELECT number n , value k
FROM testtable
GROUP BY number, value
) a
GROUP BY n
HAVING COUNT(n) = 1
You can try this
SELECT NUMBER,MAX(VALUE) AS VALUE FROM TESTTABLE
GROUP BY NUMBER
HAVING MAX(VALUE)=MIN(VALUE)
You can try also this:
SELECT DISTINCT t.number, t.value
FROM testtable t
LEFT JOIN testtable t_other
ON t.number = t_other.number AND t.value <> t_other.value
WHERE t_other.number IS NULL
Another alternative using exists.
select distinct num, val from testtable a
where not exists (
select 1 from testtable b
where a.num = b.num
and a.val <> b.val
)
http://sqlfiddle.com/#!9/dd080dd/5
I have a large data set with duplicate reference numbers (reference duplications range from 0 to 37 times). I want to count the number of references only where all instances are null in two columns. So using the table below, the code should return 1 because only Reference Code 3 has all null values, and the duplicates should only be counted once.
I would be grateful for any help.
This involves two steps: (1) isolate all the distinct pairs of values that only have null; (2) count each one once. One way to express this in a query is:
SELECT COUNT(*) FROM
(
SELECT refnum FROM #ref
GROUP BY refnum
HAVING MIN(colA) IS NULL
AND MIN(colB) IS NULL;
) AS x;
Use aggregation to get the codes:
select code
from t
group by code
having max(a) is null and max(b) is null;
If you want the count, use a subquery:
select count(*)
from (select code
from t
group by code
having max(a) is null and max(b) is null
) t;
With conditional aggregation:
select
refcode
from referencecodes
group by refcode
having sum(case when (a is null and b is null) then 0 else 1 end) = 0
The above will return the codes with only null values in a and b.
If you want the number of codes:
select count(r.refcode) from (
select
refcode
from referencecodes
group by refcode
having sum(case when (a is null and b is null) then 0 else 1 end) = 0
) r
Or with EXISTS:
select
count(distinct r.refcode)
from referencecodes r
where not exists (
select 1 from referencecodes
where (refcode = r.refcode) and (a is not null or b is not null)
)
See the demo
For example:
This is the original result
Alpha Beta
A 1
B 2
B 3
C 4
After Order by the number of Alpha, this is the result I want
Alpha Beta
B 2
B 3
A 1
C 4
I tried to use GroupBy and OrderBy, but ACCESS always ask me to include all columns.
Why is 'B' placed before 'A' ? I don't understand this order..
Any way, doesn't seem like you need a group by, not from your data sample, but for your desired result you can use CASE EXPRESSION :
SELECT t.alpha,t.beta FROM YourTable t
ORDER BY CASE WHEN t.alpha = 'B' THEN 1 ELSE 0 END DESC,
t.aplha,
t.beta
EDIT: Use this query:
SELECT t.alpha,t.beta FROM YourTable t
INNER JOIN(SELECT s.alpha,count(*) as cnt
FROM YourTable s
GROUP BY s.alpha) t2
ON(t.aplha = t2.alpha)
ORDER BY t2.cnt,t.alpha,t.beta
The query counts number of rows for every distinct Alpha and sorts. General Sql, tweak for ACCESS if needed.
SELECT t1.alpha,t1.beta
FROM t t1
JOIN (
SELECT t2.alpha, count(t2.*) AS n FROM t t2 GROUP BY t2.alpha
) t3 ON t3.alpha = t1.alpha
ORDER BY t3.n, t1.alpha, t1.beta
In the result of an SQL Select command I have two rows:
A | B
B | A
A|B and B|A means the same to me. I want, that only one of them would be selected in an SQL command.
How can I do that?
I have a select command , I join it self (natural join), like this:
SELECT a.coloumn ,b.coloumn
FROM table a,table b
where .... (not important)
and b.coloumn IN (
SELECT coloumn
FROM table
where ... (the same like above)
)
and b.coloumn != a.coloumn ;
And after that I have multiple coloumns.
You neither told us your column names nor your table name, but assuming you have two columns A and B in a table named the_table then the following will do:
select distinct least(a,b), greatest(a,b)
from the_table;
If you want to group by them using standard SQL:
select (case when a < b then a else b end) as a,
(case when a < b then b else a end) as b,
count(*) as cnt
from table t
group by (case when a < b then a else b end),
(case when a < b then b else a end);
Oracle supports the greatest() and least() functions, but not all databases do.
Another possible solution is:
select a, b from the_table
union
select b, a from the_table
This would work fine even if there are NULL values.
I have a table like
id contact value
1 A 2
2 A 3
3 B 2
4 B 3
5 B 4
6 C 2
Now I would like to get the common maximum value for a given set of contacts.
For example:
if my contact set was {A,B} it would return 3;
for the set {A,C} it would return 2
for the set {B} it would return 4
What SQL statement(s) can do this?
Try this:
SELECT value, count(distinct contact) as cnt
FROM my_table
WHERE contact IN ('A', 'C')
GROUP BY value
HAVING cnt = 2
ORDER BY value DESC
LIMIT 1
This is MySQL syntax, may differ for your database. The number (2) in HAVING clause is the number of elements in set.
SELECT max(value) FROM table WHERE contact IN ('A', 'C')
Edit: max common
declare #contacts table ( contact nchar(10) )
insert into #contacts values ('a')
insert into #contacts values ('b')
select MAX(value)
from MyTable
where (select COUNT(*) from #contacts) =
(select COUNT(*)
from MyTable t
join #contacts c on c.contact = t.contact
where t.value = MyTable.value)
Most will tell you to use:
SELECT MAX(t.value)
FROM TABLE t
WHERE t.contact IN ('A', 'C')
GROUP BY t.value
HAVING COUNT(DISTINCT t.*) = 2
Couple of caveats:
The DISTINCT is key, otherwise you could have two rows of t.contact = 'A'.
The number of COUNT(DISTINCT t.*) has to equal the number of values specified in the IN clause
My preference is to use JOINs:
SELECT MAX(t.value)
FROM TABLE t
JOIN TABLE t2 ON t2.value = t.value AND t2.contact = 'C'
WHERE t.contact = 'A'
The downside to this is that you have to do a self join (join to the same table) for every criteria (contact value in this case).