SQL filtering query based on number of related rows
I have trouble wrapping my head around this problem.
After processing some queries I end up with a result of this kind:
SELECT col1, col2 FROM Whatever;
col1 col2
1 100
2 200
3 200
2 100
And I want to pull out 2 out of this, as 2 is the only value of col1 such that it corresponds to every existing value of col2 (100 and 200). If there was another row, say, 4 400 then I would want an empty result, as there would be no rows fulfilling this condition.
I was thinking ALL could help me, but then I realised that it's useless. I'd appreciate even athe slightest hint as to what to read.
Thanks in advance.
UPD: After some digging I came to conclusion that I need relational division, i.e.
Whatever <relational division> SELECT DISTINCT col2 FROM Whatever
sql
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
add a comment |
I have trouble wrapping my head around this problem.
After processing some queries I end up with a result of this kind:
SELECT col1, col2 FROM Whatever;
col1 col2
1 100
2 200
3 200
2 100
And I want to pull out 2 out of this, as 2 is the only value of col1 such that it corresponds to every existing value of col2 (100 and 200). If there was another row, say, 4 400 then I would want an empty result, as there would be no rows fulfilling this condition.
I was thinking ALL could help me, but then I realised that it's useless. I'd appreciate even athe slightest hint as to what to read.
Thanks in advance.
UPD: After some digging I came to conclusion that I need relational division, i.e.
Whatever <relational division> SELECT DISTINCT col2 FROM Whatever
sql
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
Tag your question with the database you are using.
– Gordon Linoff
Nov 21 '18 at 16:23
@GordonLinoff I'm interested specifically in vanilla SQL, not the implementations of it. I don't want use any implementation-specific stuff.
– Всеволод Тимченко
Nov 21 '18 at 16:32
@YogeshSharma WhyHAVING COUNT(*) > 1though? There's nothing in my question that implies anything related to count larger than 1.
– Всеволод Тимченко
Nov 21 '18 at 16:33
add a comment |
I have trouble wrapping my head around this problem.
After processing some queries I end up with a result of this kind:
SELECT col1, col2 FROM Whatever;
col1 col2
1 100
2 200
3 200
2 100
And I want to pull out 2 out of this, as 2 is the only value of col1 such that it corresponds to every existing value of col2 (100 and 200). If there was another row, say, 4 400 then I would want an empty result, as there would be no rows fulfilling this condition.
I was thinking ALL could help me, but then I realised that it's useless. I'd appreciate even athe slightest hint as to what to read.
Thanks in advance.
UPD: After some digging I came to conclusion that I need relational division, i.e.
Whatever <relational division> SELECT DISTINCT col2 FROM Whatever
sql
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
I have trouble wrapping my head around this problem.
After processing some queries I end up with a result of this kind:
SELECT col1, col2 FROM Whatever;
col1 col2
1 100
2 200
3 200
2 100
And I want to pull out 2 out of this, as 2 is the only value of col1 such that it corresponds to every existing value of col2 (100 and 200). If there was another row, say, 4 400 then I would want an empty result, as there would be no rows fulfilling this condition.
I was thinking ALL could help me, but then I realised that it's useless. I'd appreciate even athe slightest hint as to what to read.
Thanks in advance.
UPD: After some digging I came to conclusion that I need relational division, i.e.
Whatever <relational division> SELECT DISTINCT col2 FROM Whatever
sql
sql
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
edited Nov 21 '18 at 18:53
Всеволод Тимченко
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
asked Nov 21 '18 at 16:21
Всеволод ТимченкоВсеволод Тимченко
10211
10211
Tag your question with the database you are using.
– Gordon Linoff
Nov 21 '18 at 16:23
@GordonLinoff I'm interested specifically in vanilla SQL, not the implementations of it. I don't want use any implementation-specific stuff.
– Всеволод Тимченко
Nov 21 '18 at 16:32
@YogeshSharma WhyHAVING COUNT(*) > 1though? There's nothing in my question that implies anything related to count larger than 1.
– Всеволод Тимченко
Nov 21 '18 at 16:33
add a comment |
Tag your question with the database you are using.
– Gordon Linoff
Nov 21 '18 at 16:23
@GordonLinoff I'm interested specifically in vanilla SQL, not the implementations of it. I don't want use any implementation-specific stuff.
– Всеволод Тимченко
Nov 21 '18 at 16:32
@YogeshSharma WhyHAVING COUNT(*) > 1though? There's nothing in my question that implies anything related to count larger than 1.
– Всеволод Тимченко
Nov 21 '18 at 16:33
Tag your question with the database you are using.
– Gordon Linoff
Nov 21 '18 at 16:23
Tag your question with the database you are using.
– Gordon Linoff
Nov 21 '18 at 16:23
@GordonLinoff I'm interested specifically in vanilla SQL, not the implementations of it. I don't want use any implementation-specific stuff.
– Всеволод Тимченко
Nov 21 '18 at 16:32
@GordonLinoff I'm interested specifically in vanilla SQL, not the implementations of it. I don't want use any implementation-specific stuff.
– Всеволод Тимченко
Nov 21 '18 at 16:32
@YogeshSharma Why
HAVING COUNT(*) > 1 though? There's nothing in my question that implies anything related to count larger than 1.– Всеволод Тимченко
Nov 21 '18 at 16:33
@YogeshSharma Why
HAVING COUNT(*) > 1 though? There's nothing in my question that implies anything related to count larger than 1.– Всеволод Тимченко
Nov 21 '18 at 16:33
add a comment |
1 Answer
1
active
oldest
votes
One method uses window functions:
select col1, col2
from (select col1, col2,
count(distinct col2) over () as num_col2,
count(distinct col2) over (partition by col1) as num_col2_per_col1
from whatever
) t
where num_col2 = num_col2_per_col1;
Not all databases support count(distinct) as a window function. There are pretty simply work-arounds, if that is necessary, but count(distinct) as a window function is standard SQL.
If you only want "2" and not all the rows, then use select distinct col1.
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
1
.great answer!!
– stack0114106
Jan 16 at 2:56
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
One method uses window functions:
select col1, col2
from (select col1, col2,
count(distinct col2) over () as num_col2,
count(distinct col2) over (partition by col1) as num_col2_per_col1
from whatever
) t
where num_col2 = num_col2_per_col1;
Not all databases support count(distinct) as a window function. There are pretty simply work-arounds, if that is necessary, but count(distinct) as a window function is standard SQL.
If you only want "2" and not all the rows, then use select distinct col1.
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
1
.great answer!!
– stack0114106
Jan 16 at 2:56
add a comment |
One method uses window functions:
select col1, col2
from (select col1, col2,
count(distinct col2) over () as num_col2,
count(distinct col2) over (partition by col1) as num_col2_per_col1
from whatever
) t
where num_col2 = num_col2_per_col1;
Not all databases support count(distinct) as a window function. There are pretty simply work-arounds, if that is necessary, but count(distinct) as a window function is standard SQL.
If you only want "2" and not all the rows, then use select distinct col1.
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
1
.great answer!!
– stack0114106
Jan 16 at 2:56
add a comment |
One method uses window functions:
select col1, col2
from (select col1, col2,
count(distinct col2) over () as num_col2,
count(distinct col2) over (partition by col1) as num_col2_per_col1
from whatever
) t
where num_col2 = num_col2_per_col1;
Not all databases support count(distinct) as a window function. There are pretty simply work-arounds, if that is necessary, but count(distinct) as a window function is standard SQL.
If you only want "2" and not all the rows, then use select distinct col1.
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
One method uses window functions:
select col1, col2
from (select col1, col2,
count(distinct col2) over () as num_col2,
count(distinct col2) over (partition by col1) as num_col2_per_col1
from whatever
) t
where num_col2 = num_col2_per_col1;
Not all databases support count(distinct) as a window function. There are pretty simply work-arounds, if that is necessary, but count(distinct) as a window function is standard SQL.
If you only want "2" and not all the rows, then use select distinct col1.
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
edited Nov 21 '18 at 16:31
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
answered Nov 21 '18 at 16:25
Gordon LinoffGordon Linoff
789k35313418
789k35313418
1
.great answer!!
– stack0114106
Jan 16 at 2:56
add a comment |
1
.great answer!!
– stack0114106
Jan 16 at 2:56
1
1
.great answer!!
– stack0114106
Jan 16 at 2:56
.great answer!!
– stack0114106
Jan 16 at 2:56
add a comment |
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Tag your question with the database you are using.
– Gordon Linoff
Nov 21 '18 at 16:23
@GordonLinoff I'm interested specifically in vanilla SQL, not the implementations of it. I don't want use any implementation-specific stuff.
– Всеволод Тимченко
Nov 21 '18 at 16:32
@YogeshSharma Why
HAVING COUNT(*) > 1though? There's nothing in my question that implies anything related to count larger than 1.– Всеволод Тимченко
Nov 21 '18 at 16:33