SQL. how to compare values and from two table, and report per-row results - sql

Question

I have two Tables.
table A
id name Size
===================
1 Apple 7
2 Orange 15
3 Banana 22
4 Kiwi 2
5 Melon 28
6 Peach 9
And Table B
id size
==============
1 14
2 5
3 31
4 9
5 1
6 16
7 7
8 25
My desired result will be (add one column to Table A, which is the number of rows in Table B that have size smaller than Size in Table A)
id name Size Num.smaller.in.B
==============================
1 Apple 7 2
2 Orange 15 5
3 Banana 22 6
4 Kiwi 2 1
5 Melon 28 7
6 Peach 9 3
Both Table A and B are pretty huge. Is there a clever way of doing this. Thanks

Answer 1

Use this query it's helpful
SELECT id,
name,
Size,
(Select count(*) From TableB Where TableB.size<Size)
FROM TableA

Answer 2

The standard way to get your result involves a non-equi-join, which will be a product join in Explain. First duplicating 20,000 rows, followed by 7,000,000 * 20,000 comparisons and a huge intermediate spool before the count.
There's a solution based on OLAP-functions which is usually quite efficient:
SELECT dt.*,
-- Do a cumulative count of the rows of table #2
-- sorted by size, i.e. count number of rows with a size #2 less size #1
Sum(CASE WHEN NAME = '' THEN 1 ELSE 0 end)
Over (ORDER BY SIZE, NAME DESC ROWS Unbounded Preceding)
FROM
( -- mix the rows of both tables, an empty name indicates rows from table #2
SELECT id, name, size
FROM a
UNION ALL
SELECT id, '', size
FROM b
) AS dt
-- only return the rows of table #1
QUALIFY name <> ''
If there are multiple rows with the same size in table #2 you better count before the Union to reduce the size:
SELECT dt.*,
-- Do a cumulative sum of the counts of table #2
-- sorted by size, i.e. count number of rows with a size #2 less size #1
Sum(CASE WHEN NAME ='' THEN id ELSE 0 end)
Over (ORDER BY SIZE, NAME DESC ROWS Unbounded Preceding)
FROM
( -- mix the rows of both tables, an empty name indicates rows from table #2
SELECT id, name, size
FROM a
UNION ALL
SELECT Count(*), '', SIZE
FROM b
GROUP BY SIZE
) AS dt
-- only return the rows of table #1
QUALIFY NAME <> ''

Answer 3

There is no clever way of doing that, you just need to join the tables like this:
select a.*, b.size
from TableA a join TableB b on a.id = b.id
To improve performance you'll need to have indexes on the id columns.

Answer 4

maybe
select
id,
name,
a.Size,
sum(cnt) as sum_cnt
from
a inner join
(select size, count(*) as cnt from b group by size) s on
s.size < a.size
group by id,name,a.size
if you're working with large tables. Indexing table b's size field could help. I'm also assuming the values in table B converge, that there's many duplicates you don't care about, other than you want to count them.
sqlfiddle

Answer 5

#Ritesh solution is perfectly correct, another similar solution is using CROSS JOIN as shown below
use tempdb
create table dbo.A (id int identity, name varchar(30), size int );
create table dbo.B (id int identity, size int);
go
insert into dbo.A (name, size)
values ('Apple', 7)
,('Orange', 15)
,('Banana', 22)
,('Kiwi', 2 )
,('Melon', 28)
,('Peach', 6 )
insert into dbo.B (size)
values (14), (5),(31),(9),(1),(16), (7),(25)
go
-- using cross join
select a.*, t.cnt
from dbo.A
cross apply (select cnt=count(*) from dbo.B where B.size < A.size) T(cnt)

Answer 6

try this query
SELECT
A.id,A.name,A.size,Count(B.size)
from A,B
where A.size>B.size
group by A.size
order by A.id;