How to create a SQL Server function to join multiple rows from a subquery into a single delimited field

Question

To illustrate  assume that I have two tables as follows   VehicleID Name 1         Chuck 2         Larry  LocationID VehicleID City 1          1         New York 2          1         Seattle 3          1         Vancouver 4          2         Los Angeles 5          2         Houston   I want to write a query to return the following results   VehicleID Name    Locations 1         Chuck   New York  Seattle  Vancouver 2         Larry   Los Angeles  Houston   I know that this can be done using server side cursors  ie   DECLARE  VehicleID int DECLARE  VehicleName varchar 100  DECLARE  LocationCity varchar 100  DECLARE  Locations varchar 4000  DECLARE  Results TABLE     VehicleID int   Name varchar 100    Locations varchar 4000     DECLARE VehiclesCursor CURSOR FOR SELECT    VehicleID     Name  FROM  Vehicles   OPEN VehiclesCursor  FETCH NEXT FROM VehiclesCursor INTO    VehicleID    VehicleName WHILE   FETCH STATUS   0 BEGIN    SET  Locations         DECLARE LocationsCursor CURSOR FOR   SELECT      City    FROM  Locations    WHERE  VehicleID     VehicleID    OPEN LocationsCursor    FETCH NEXT FROM LocationsCursor INTO      LocationCity   WHILE   FETCH STATUS   0   BEGIN     SET  Locations    Locations    LocationCity      FETCH NEXT FROM LocationsCursor INTO        LocationCity   END   CLOSE LocationsCursor   DEALLOCATE LocationsCursor    INSERT INTO  Results  VehicleID  Name  Locations  SELECT  VehicleID   Name   Locations  END      CLOSE VehiclesCursor DEALLOCATE VehiclesCursor  SELECT   FROM  Results   However  as you can see  this requires a great deal of code   What I would like is a generic function that would allow me to do something like this   SELECT VehicleID        Name        JOIN SELECT City FROM Locations WHERE VehicleID   Vehicles VehicleID        AS Locations FROM Vehicles   Is this possible   Or something similar

User · Answer

The below code will work for Sql Server 2000 2005 2008  CREATE FUNCTION fnConcatVehicleCities  VehicleId SMALLINT  RETURNS VARCHAR 1000  AS BEGIN   DECLARE  csvCities VARCHAR 1000    SELECT  csvCities   COALESCE  csvCities               COALESCE City       FROM Vehicles    WHERE VehicleId    VehicleId    return  csvCities END  --   Once the User defined function is created then run the below sql  SELECT VehicleID        dbo fnConcatVehicleCities VehicleId  AS Locations FROM Vehicles GROUP BY VehicleID

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From what I can see FOR XML  as posted earlier  is the only way to do it if you want to also select other columns  which I d guess most would  as the OP does  Using COALESCE  var    does not allow inclusion of other columns   Update  Thanks to programmingsolutions net there is a way to remove the  trailing  comma to  By making it into a leading comma and using the STUFF function of MSSQL you can replace the first character  leading comma  with an empty string as below   stuff       select       Column       from Table          inner where inner Id   outer Id       for xml path        1 1     as Values

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If you re running SQL Server 2005  you can write a custom CLR aggregate function to handle this   C  version   using System  using System Data  using System Data SqlClient  using System Data SqlTypes  using System Text  using Microsoft SqlServer Server   Serializable   Microsoft SqlServer Server SqlUserDefinedAggregate Format UserDefined MaxByteSize 8000   public class CSV IBinarySerialize       private StringBuilder Result      public void Init             this Result   new StringBuilder               public void Accumulate SqlString Value            if  Value IsNull  return          this Result Append Value Value  Append                 public void Merge CSV Group            this Result Append Group Result             public SqlString Terminate             return new SqlString this Result ToString               public void Read System IO BinaryReader r            this Result   new StringBuilder r ReadString               public void Write System IO BinaryWriter w            w Write this Result ToString

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In SQL Server 2005  SELECT Stuff     SELECT N       Name FROM Names FOR XML PATH     TYPE     value  text   1    nvarchar max    1 2 N        In SQL Server 2016  you can use the FOR JSON syntax  i e    SELECT per ID  Emails   JSON VALUE     REPLACE        SELECT     em Email FROM Email em WHERE em Person   per ID FOR JSON PATH                            0        FROM Person per   And the result will become  Id  Emails 1   abc gmail com 2   NULL 3   def gmail com  xyz gmail com   This will work even your data contains invalid XML characters  the            is safe because if you data contain             it will be escaped to               You can replace      with any string separator    And in SQL Server 2017  Azure SQL Database  You can use the new STRING AGG function

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In a single SQL query  without using the FOR XML clause  A Common Table Expression is used to recursively concatenate the results   -- rank locations by incrementing lexicographical order WITH RankedLocations AS     SELECT     VehicleID      City      ROW NUMBER   OVER           PARTITION BY VehicleID          ORDER BY City       Rank   FROM     Locations    -- concatenate locations using a recursive query --  Common Table Expression  Concatenations AS     -- for each vehicle  select the first location   SELECT     VehicleID      CONVERT nvarchar MAX   City  Cities      Rank   FROM     RankedLocations   WHERE     Rank   1    -- then incrementally concatenate with the next location   -- this will return intermediate concatenations that will be    -- filtered out later on   UNION ALL    SELECT     c VehicleID       c Cities          l City  Cities      l Rank   FROM     Concatenations c -- this is a recursion      INNER JOIN RankedLocations l ON         l VehicleID   c VehicleID          AND l Rank   c Rank   1    -- rank concatenation results by decrementing length  --  rank 1 will always be for the longest concatenation  RankedConcatenations AS     SELECT     VehicleID      Cities      ROW NUMBER   OVER           PARTITION BY VehicleID          ORDER BY Rank DESC       Rank   FROM      Concatenations   -- main query SELECT   v VehicleID    v Name    c Cities FROM   Vehicles v   INNER JOIN RankedConcatenations c ON      c VehicleID   v VehicleID      AND c Rank   1

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VERSION NOTE  You must be using SQL Server 2005 or greater with Compatibility Level set to 90 or greater for this solution   See this MSDN article for the first example of creating a user-defined aggregate function that concatenates a set of string values taken from a column in a table   My humble recommendation would be to leave out the appended comma so you can use your own ad-hoc delimiter  if any   Referring to the C  version of Example 1   change   this intermediateResult Append value Value  Append           to   this intermediateResult Append value Value     And  change   output   this intermediateResult ToString 0  this intermediateResult Length - 1       to   output   this intermediateResult ToString      That way when you use your custom aggregate  you can opt to use your own delimiter  or none at all  such as   SELECT dbo CONCATENATE column1        from table1   NOTE  Be careful about the amount of the data you attempt to process in your aggregate  If you try to concatenate thousands of rows or many very large datatypes you may get a  NET Framework error stating   t he buffer is insufficient

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Note that Matt s code will result in an extra comma at the end of the string  using COALESCE  or ISNULL for that matter  as shown in the link in Lance s post uses a similar method but doesn t leave you with an extra comma to remove   For the sake of completeness  here s the relevant code from Lance s link on sqlteam com   DECLARE  EmployeeList varchar 100  SELECT  EmployeeList   COALESCE  EmployeeList                    CAST EmpUniqueID AS varchar 5   FROM SalesCallsEmployees WHERE SalCal UniqueID   1

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I ve found a solution by creating the following function   CREATE FUNCTION  dbo   JoinTexts       delimiter VARCHAR 20       whereClause VARCHAR 1    RETURNS VARCHAR MAX  AS  BEGIN     DECLARE  Texts VARCHAR MAX       SELECT   Texts   COALESCE  Texts    delimiter        T Texto     FROM    SomeTable AS T     WHERE   T SomeOtherColumn    whereClause      RETURN  Texts END GO   Usage   SELECT dbo JoinTexts         Y

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With the other answers  the person reading the answer must be aware of the vehicle table and create the vehicle table and data to test a solution     Below is an example that uses SQL Server  Information Schema Columns  table   By using this solution  no tables need to be created or data added   This example creates a comma separated list of column names for all tables in the database   SELECT     Table Name      STUFF           SELECT       Column Name         FROM INFORMATION SCHEMA Columns Columns         WHERE Tables Table Name   Columns Table Name         ORDER BY Column Name         FOR XML PATH        1  1          Columns FROM INFORMATION SCHEMA Columns Tables GROUP BY TABLE NAME

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Try this query  SELECT v VehicleId  v Name  ll LocationList FROM Vehicles v  LEFT JOIN       SELECT       DISTINCT         VehicleId          REPLACE              REPLACE                  REPLACE                                                SELECT City as c                          FROM Locations x                          WHERE x VehicleID   l VehicleID FOR XML PATH                                                      lt  c gt  lt c gt                                           lt c gt                               lt  c gt                 AS LocationList     FROM Locations l   ll ON ll VehicleId   v VehicleId

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I don t belive there s a way to do it within one query  but you can play tricks like this with a temporary variable   declare  s varchar max  set  s      select  s    s   City       from Locations  select  s   It s definitely less code than walking over a cursor  and probably more efficient

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Mun s answer didn t work for me so I made some changes to that answer to get it to work  Hope this helps someone  Using SQL Server 2012   SELECT  VehicleID          Name         STUFF  SELECT DISTINCT       CONVERT VARCHAR City            FROM  Location            WHERE  VehicleID   Vehicle VehicleID            FOR XML PATH        1  2      AS Locations FROM  Vehicle

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If you re using SQL Server 2005  you could use the FOR XML PATH command   SELECT  VehicleID          Name          STUFF  SELECT CAST         City  AS VARCHAR MAX             FROM  Location            WHERE  VehicleID   Vehicle VehicleID            FOR XML PATH        1  2       AS Locations FROM  Vehicle    It s a lot easier than using a cursor  and seems to work fairly well

[sql] How to create a SQL Server function to "join" multiple rows from a subquery into a single delimited field?

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