Select query select based on a priority - sql

Question

Someone please change my title to better reflect what I am trying to ask.
I have a table like
Table (id, value, value_type, data)
ID is NOT unique. There is no unique key.
value_type has two possible values, let's say A and B.
Type B is better than A, but often not available.
For each id if any records with value_type B exists, I want all the records with that id and value_type B.
If no record for that id with value_Type B exists I want all records with that id and value_type A.
Notice that if B exists for that id I don't want records with type A.
I currently do this with a series of temp tables. Is there a single select statement (sub queries OK) that can do the job?
Thanks so much!
Additional details:
SQL Server 2005

Answer 1

RANK, rather than ROW_NUMBER, because you want ties (those with the same B value) to have the same rank value:
WITH summary AS (
SELECT t.*,
RANK() OVER (PARTITION BY t.id
ORDER BY t.value_type DESC) AS rank
FROM TABLE t
WHERE t.value_type IN ('A', 'B'))
SELECT s.id,
s.value,
s.value_type,
s.data
FROM summary s
WHERE s.rank = 1
Non CTE version:
SELECT s.id,
s.value,
s.value_type,
s.data
FROM (SELECT t.*,
RANK() OVER (PARTITION BY t.id
ORDER BY t.value_type DESC) AS rank
FROM TABLE t
WHERE t.value_type IN ('A', 'B')) s
WHERE s.rank = 1
WITH test AS (
SELECT 1 AS id, 'B' AS value_type
UNION ALL
SELECT 1, 'B'
UNION ALL
SELECT 1, 'A'
UNION ALL
SELECT 2, 'A'
UNION ALL
SELECT 2, 'A'),
summary AS (
SELECT t.*,
RANK() OVER (PARTITION BY t.id
ORDER BY t.value_type DESC) AS rank
FROM test t)
SELECT *
FROM summary
WHERE rank = 1
I get:
id value_type rank
----------------------
1 B 1
1 B 1
2 A 1
2 A 1

Answer 2

SELECT *
FROM table
WHERE value_type = B
UNION ALL
SELECT *
FROM table
WHERE ID not in (SELECT distinct id
FROM table
WHERE value_type = B)

Answer 3

The shortest query to do the job I can think of:
SELECT TOP 1 WITH TIES *
FROM #test
ORDER BY Rank() OVER (PARTITION BY id ORDER BY value_type DESC)
This is about 50% worse on CPU as OMG Ponies' and Christoperous 5000's solutions, but the same number of reads. It's the extra sort that is making it take more CPU.
The best-performing original query I've come up with so far is:
SELECT *
FROM #test
WHERE value_type = 'B'
UNION ALL
SELECT *
FROM #test T1
WHERE NOT EXISTS (
SELECT *
FROM #test T2
WHERE
T1.id = T2.id
AND T2.value_type = 'B'
)
This consistently beats all the others presented on CPU by about 1/3rd (the others are about 50% more) but has 3x the number of reads. The duration on this query is often 2/3rds the time of all the others. I consider it a good contender.
Indexes and data types could change everything.

Answer 4

declare #test as table(
id int , value [nvarchar](255),value_type [nvarchar](255),data int)
INSERT INTO #test
SELECT 1, 'X', 'A',1 UNION
SELECT 1, 'X', 'A',2 UNION
SELECT 1, 'X', 'A',3 UNION
SELECT 1, 'X', 'A',4 UNION
SELECT 2, 'X', 'A',5 UNION
SELECT 2, 'X', 'B',6 UNION
SELECT 2, 'X', 'B',7 UNION
SELECT 2, 'X', 'A',8 UNION
SELECT 2, 'X', 'A',9
SELECT * FROM #test x
INNER JOIN
(SELECT id, MAX(value_type) as value_type FROM
#test GROUP BY id) as y
ON x.id = y.id AND x.value_type = y.value_type

Answer 5

Try this (MSSQL).
Select id, value_typeB, null
from myTable
where value_typeB is not null
Union All
Select id, null, value_typeA
from myTable
where value_typeB is null and value_typeA is not null

Answer 6

Perhaps something like this:
select * from mytable
where id in (select distinct id where value_type = "B")
union
select * from mytable
where id in (select distinct id where value_type = "A"
and id not in (select distinct id where value_type = "B"))

Answer 7

This uses a union, combining all records of value B with all records that have only A values:
SELECT *
FROM mainTable
WHERE value_type = B
GROUP BY value_type UNION SELECT *
FROM mainTable
WHERE value_type = A
AND id NOT IN(SELECT *
FROM mainTable
WHERE value_type = B);