How to concatenate strings from multiple rows in o

问题:

I have a query with the following result: query:

SELECT Tasks.TaskId, Comments.Comment, comments.timespent       
FROM   comments
INNER JOIN tasks ON comments.entityid = tasks.taskid                
WHERE  ( comments.entity = 1 ) 
GROUP  BY Tasks.TaskId, Comments.Comment, comments.timespent

Result:

TaskID  Comment  TimeSpent
__________________________
111754    C1        4
111754    C2        1
111754    C3       79

Please tell me how should I write my query to get the result as follows:

TaskID  Comment          TimeSpent
__________________________________
111754  ,C1,C2,C3           84

Thanks in advance.

回答1:

Here's the working SQL Fiddle: http://sqlfiddle.com/#!3/3597a/3

Here's the actual working SQL.

SELECT Tasks.TaskId, SUBSTRING(
(SELECT ',' + Comments.Comment
FROM Comments
INNER JOIN tasks ON comments.entityid = tasks.taskid
FOR XML PATH('')),2,200000) AS Comments
, SUM(comments.timespent) AS TimeSpent      
FROM   comments
INNER JOIN tasks ON comments.entityid = tasks.taskid                
WHERE  ( comments.entity = 1 ) 
GROUP  BY Tasks.TaskId

Create Table and Populate Data

CREATE TABLE Tasks
(
  TaskID NVARCHAR(20) NOT NULL,
);

CREATE TABLE Comments
( 
  Entity  INT NOT NULL,
  EntityID NVARCHAR(20) NOT NULL,
  Comment NVARCHAR(50) NOT NULL,
  TimeSpent INT NOT NULL
);


INSERT INTO Tasks VALUES
( '111754' );

INSERT INTO Comments VALUES
(1,'111754', 'C1',4 ),
(1,'111754', 'C2',1 ),
(1,'111754', 'C3',79 );

Execute SQL

SELECT Tasks.TaskId, SUBSTRING(
(SELECT ',' + Comments.Comment
FROM Comments
INNER JOIN tasks ON comments.entityid = tasks.taskid
FOR XML PATH('')),2,200000) AS Comments
, SUM(comments.timespent) AS TimeSpent     
FROM   comments
INNER JOIN tasks ON comments.entityid = tasks.taskid                
WHERE  comments.entity = 1 
GROUP  BY Tasks.TaskId

View Results.

TASKID  COMMENTS    TIMESPENT
111754  C1,C2,C3    84

回答2:

You should look into FOR XML PATH.

回答3:

You can do with CROSS APPLY with XML Path such as:

   `
 Select *
   from table1 t1
     CROSS APPLY
      (
 SELECT
    [text()] = t.[Name] + '; '
    FROM table2 t2
    WHERE t1.[Id] = t2.[Id]
   ORDER BY t2.name
   FOR XML PATH('')
       ) a (Type)
`

回答4:

Ok, this is a bit more complicated but it doesn't use xml, and it can be used with other databases than sql server:

    WITH orig
         AS (SELECT 1 AS f1, 'C11' AS f2
             UNION ALL
             SELECT 1 AS f1, 'C12' AS f2
             UNION ALL
             SELECT 1 AS f1, 'C13' AS f2
             UNION ALL
             SELECT 2 AS f1, 'C21' AS f2
             UNION ALL
             SELECT 2 AS f1, 'C22' AS f2
             UNION ALL
             SELECT 2 AS f1, 'C23' AS f2
             UNION ALL
             SELECT 3 AS f1, 'C31' AS f2)
       , orig2 AS (SELECT DISTINCT f1, f2 FROM orig)
       , orig3 AS (SELECT f1, f2, row_number() OVER(PARTITION BY f1 ORDER BY f2) AS RowNum FROM orig2)
       , orig4
         -- Use recursion to concatenate the fields
         AS (SELECT f1, CONVERT(VARCHAR(MAX), f2) AS val, rownum
               FROM orig3
              WHERE RowNum = 1
             UNION ALL
             SELECT orig4.f1, orig4.val + ', ' + orig3.f2 AS val, orig3.rownum
               FROM orig4
                    INNER JOIN orig3
                      ON orig4.RowNum + 1 = orig3.RowNum
                     AND orig4.f1 = orig3.f1)
    SELECT *
      FROM orig4
     -- select only the rows that match the maximum rownum
     WHERE NOT EXISTS
             (SELECT 1
                FROM orig4 o44
               WHERE o44.f1 = orig4.f1
                 AND o44.rownum > orig4.rownum)

Another approach that works only for sql server would be to build an aggregate CLR function that concatenates the values: http://msdn.microsoft.com/en-us/library/91e6taax%28v=vs.90%29.aspx.

If you came across this article but you use oracle, you have the option to use the query above or define a custom aggregate function in pl/sql (http://docs.oracle.com/cd/B28359_01/appdev.111/b28425/aggr_functions.htm).