Missing GROUP_CONCAT Implementation

PDOException: SQLSTATE[42000]: [Microsoft][SQL Server Native Client 11.0][SQL Server]'GROUP_CONCAT' is not a recognized aggregate function.: SELECT TOP(25) pmi.[thread_id] AS [thread_id], MIN(pm.subject) AS subject, MAX(pm.timestamp) AS last_updated, MAX(pm.has_tokens) AS has_tokens, SUM(pmi.is_new) AS is_new, (SELECT GROUP_CONCAT(DISTINCT CONCAT(pmia.type, '_', pmia.recipient)) FROM {pm_index} pmia WHERE pmia.type <> 'hidden' AND pmia.thread_id = pmi.thread_id AND pmia.recipient <> :current) AS participants, pmi.thread_id AS _field_0 FROM {pm_message} pm INNER JOIN {pm_index} pmi ON pm.mid = pmi.mid INNER JOIN {pm_tags_index} pmti ON pmti.thread_id = pmi.thread_id AND pmti.uid = pmi.recipient AND pmi.type IN ('user', 'hidden') WHERE ( ([pmi].[recipient] = :db_condition_placeholder_0) AND ([pmi].[type] IN (:db_condition_placeholder_1, :db_condition_placeholder_2)) AND ([pmi].[deleted] = :db_condition_placeholder_3) AND ([pmti].[tag_id] = :db_condition_placeholder_4) ) GROUP BY pmi.thread_id ORDER BY last_updated DESC; Array ( [:db_condition_placeholder_0] => 3 [:db_condition_placeholder_1] => hidden [:db_condition_placeholder_2] => user [:db_condition_placeholder_3] => 0 [:db_condition_placeholder_4] => 1 [:current] => 3 ) en PagerDefault->execute() (línea 79 de C:\inetpub\wwwroot\drupal_david\public\includes\pager.inc).

From this exception, SQL Server is missing the Group_Concat implementation.

Reference to possible solutions:

- http://social.msdn.microsoft.com/Forums/en-US/transactsql/thread/9508abc...
- http://groupconcat.codeplex.com/

Install GROUP_CONCAT functions and modify database.inc accrodingly:

// Add prefixes to Drupal-specific functions.
$functions = array(
'SUBSTRING',
'SUBSTRING_INDEX',
'GREATEST',
'GROUP_CONCAT',
'CONCAT',
'IF',
);

But, once this is fixed, the same module gives an error due to using the CONCAT function with 3 parameters insted of 2 (in the same SQL query that failed previously).

This can be easily fixed by modifying the default function created by the driver to accept 3 parameters, making the last two optionals:

ALTER FUNCTION [dbo].[CONCAT](@op1 sql_variant = 11, @op2 sql_variant = '',@op3 sql_variant = '') RETURNS nvarchar(4000) AS
BEGIN
DECLARE @result nvarchar(4000)
SET @result = CAST(@op1 AS nvarchar(4000)) + CAST(@op2 AS nvarchar(4000)) + CAST(@op3 AS nvarchar(4000))
RETURN @result
END

To convert all of these into a patch....

1. Modifiy the driver installer (install.inc) to include the creation of the procedures provided in GROUP_CONTACT.zip (obtained from http://groupconcat.codeplex.com/). It should also be considered that SQL SERVER 2012 has built-in GROUP_CONTACT.

2. Path "database.inc" to prefix calls to GROUP_CONTACT (->[dbo].[GROUP_CONTACT]), snippet provided.

3. Modify driver installer (install.inc) to include the new version of CONCAT wich is more flexible as to the number of parameters it can receive, and has fully backwards compatibility with old implementation.

If i find the time I will turn all of these into a decent path, in the meanwhile applying these 3 changes can server as a fix!