Getting the Next Available Row - sql

Question

How can I get a List all the JobPositionNames having the lowest jobPositionId when ContactId = 1
Tablel :
| JobPositionId | JobPositionName | JobDescriptionId | JobCategoryId | ContactId
---------------------------------------------------------------------------------
1 | Audio Cables | 1 | 1 | 1
2 |Audio Connections| 2 | 1 | 1
3 |Audio Connections| 2 | 1 | 0
4 |Audio Connections| 2 | 1 | 0
5 | Sound Board | 3 | 1 | 0
6 | Tent Pen | 4 | 3 | 0
eg the result of this table should be lines 1,3,5,6

Answer 1

I can't figure out the solution.
Only lack of something, but I can give some code for you view.
Maybe it can help you.
--create table
create table t
(
JobPositionId int identity(1,1) primary key,
JobPositionName nvarchar(100) not null,
JobDescriptionId int,
JobCategoryId int,
ContactId int
)
go
--insert values
BEGIN TRAN
INSERT INTO t VALUES ('AudioCables', 1,1,1)
INSERT INTO t VALUES ('AudioConnections',2,1,1)
INSERT INTO t VALUES ('AudioConnections',2,1,0)
INSERT INTO t VALUES ('AudioConnections',2,1,0)
INSERT INTO t VALUES ('SoundBoard',3,1,0)
INSERT INTO t VALUES ('TentPen',4,3,0)
COMMIT TRAN
GO
SELECT
Min(JobPositionId) AS JobPositionId, JobPositionName, ContactId
INTO
#tempTable
FROM
t
GROUP BY JobPositionName, ContactId
SELECT * FROM #tempTable
WHERE JobPositionId IN (
SELECT JobPositionId
FROM #tempTable
GROUP BY JobPositionName
--... lack of sth, I can't figure out ,sorry.
)
drop table t
GO

Answer 2

For per-group maximum/minimum queries you can use a null-self-join as well as strategies like subselects. This is generally faster in MySQL.
SELECT j0.JobPositionId, j0.JobPositionName, j0.ContactId
FROM Jobs AS j0
LEFT JOIN Jobs AS j1 ON j1.JobPositionName=j0.JobPositionName
AND (
(j1.ContactId<>0)<(j0.ContactId<>0)
OR ((j1.ContactId<>0)=(j0.ContactId<>0) AND j1.JobPositionId<j0.JobPositionId))
)
WHERE j1.JobPositionName IS NULL
This says, for each JobPositionName, find a row for which there exists no other row with a lower ordering value. The ordering value here is a composite [ContactId-non-zeroness, JobPositionId].
(Aside: shouldn't JobPositionName and JobCategoryId be normalised out into a table keyed on JobDescriptionId? And shouldn't unassigned ContactIds be NULL?)

Answer 3

SELECT jp.*
FROM (
SELECT JobPositionName, JobPositionId, COUNT(*) AS cnt
FROM JobPosisions
) jpd
JOIN JobPosisions jp
ON jp.JobPositionId =
IF(
cnt = 1,
jpd.JobPositionId,
(
SELECT MIN(JobPositionId)
FROM JobPositions jpi
WHERE jpi.JobPositionName = jpd.JobPositionName
AND jpi.ContactID = 0
)
)
Create an index on (JobPositionName, ContactId, JobPositionId) for this to work fast.
Note that if will not return the jobs having more than one position, neither of which has ContactID = 0