问题
I have a problem with a query. Let's say I have two tables named PersonInfo and PersonEducation. I applied join operation on these tables with StudentId and I have a result like that.
StudentIdId Name University Department Status
---------------------------------------------------------------
1 John Cambridge Computer Graduated
1 John Berkeley Mathematic Graduated
1 John Boston Economy Ongoing
It is just one example of a student (John). It shows that John graduated from 2 university and still studying in one university. University numbers can change depending on the students. My question is that how can I show these 3 row in just 1 row. I mean I want to show all education information in one row in order not to have multiple rows for one person.
Thanks in advance for your help.
回答1:
Test Data
DECLARE @TABLE TABLE (StudentIdId INT, Name VARCHAR(100), University VARCHAR(100)
, Department VARCHAR(100),[Status] VARCHAR(100))
INSERT INTO @TABLE VALUES
(1 ,'John','Cambridge','Computer' ,'Graduated'),
(1 ,'John','Berkeley' ,'Mathematic','Graduated'),
(1 ,'John','Boston' ,'Economy' ,'Ongoing'),
(2 ,'Pete','Cambridge','Computer' ,'Graduated'),
(2 ,'Pete','Berkeley' ,'Mathematic','Graduated')
Query
SELECT t.StudentIdId
,t.Name
,STUFF((SELECT ', ' + University
FROM @TABLE
WHERE StudentIdId = t.StudentIdId
FOR XML PATH(''),TYPE).value('.','NVARCHAR(MAX)'),1,2,'') AS University
,STUFF((SELECT ', ' + Department
FROM @TABLE
WHERE StudentIdId = t.StudentIdId
FOR XML PATH(''),TYPE).value('.','NVARCHAR(MAX)'),1,2,'') AS Department
,STUFF((SELECT ', ' + [Status]
FROM @TABLE
WHERE StudentIdId = t.StudentIdId
FOR XML PATH(''),TYPE).value('.','NVARCHAR(MAX)'),1,2,'') AS [Status]
FROM @TABLE t
GROUP BY t.StudentIdId ,t.Name
Result
╔═════════════╦══════╦═════════════════════════════╦═══════════════════════════════╦═══════════════════════════════╗
║ StudentIdId ║ Name ║ University ║ Department ║ Status ║
╠═════════════╬══════╬═════════════════════════════╬═══════════════════════════════╬═══════════════════════════════╣
║ 1 ║ John ║ Cambridge, Berkeley, Boston ║ Computer, Mathematic, Economy ║ Graduated, Graduated, Ongoing ║
║ 2 ║ Pete ║ Cambridge, Berkeley ║ Computer, Mathematic ║ Graduated, Graduated ║
╚═════════════╩══════╩═════════════════════════════╩═══════════════════════════════╩═══════════════════════════════╝
回答2:
It depends on what you want for the output.
- If you want to aggregate the data in PersonEducation to count the statuses, then you could join on a subquery of the PersonEducation table. There are numerous articles on how to use subqueries and how to group by fields.
Something like:
SELECT pere.StudentId
, pere.StudentName
, peri.UniversityCount
, peri.GraduatedStatusCout
, peri.OngoingStatusCount
FROM PersonInfo peri
LEFT JOIN
(SELECT StudentId
, UniversityCount = COUNT(*)
, GraduatedStatusCount = SUM(IIF(Status = 'Graduated', 1, 0))
, OngoingStatusCount = SUM(IIF(Status = 'Ongoing', 1, 0))
FROM PersonEducation
GROUP BY StudentId) pere
ON peri.StudentId = pere.StudentId;
If you want to get the last university attended, then you would need a date attended field of some sort. It is possible there are more than one universities that someone attends at the same time, so you would need rules around how to pick a winner. In these cases, though, you could get away with using a ROW_NUMBER() in an OVER() clause to order the data and filter the results.
You could concatenate the data together as described here or in any number of other articles.
来源：https://stackoverflow.com/questions/27712374/how-to-convert-multiple-rows-to-one-row-in-sql-server