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You can find a lot of debugging and deploying problems while developing applications in .NET and Visual Basic here. There are also some querying tips in SQL and typical source codes which might be useful shared here.

Add Trusted Hosts to Tableau Server

Problem: After deploying Tableau dashboards, you are not able to display the dashboard using trusted ticket method. Error returned: "Could not locate unexpired trusted ticket <ticket_number>".

Solution: Although there could be various reason for this error, you might want to check if the IP address in which the Tableau dashboard is going to be displayed, is already added to the trusted hosts in the Tableau server. If it is not yet added, add it to the trusted hosts.
Note: Make sure not to overwrite the existing trusted hosts already added previously.

Assume the host (where the Tableau dashboard is going to be displayed) is: 10.0.0.99

1. Go to the Tableau server, and look for dataserver.properties, located in C:\ProgramData\Tableau\Tableau Server\data\tabsvc\config\ (location might vary).
Search for trusted_hosts, and take note of the existing trusted hosts already added previously.
e.g. trusted_hosts=10.0.0.91, 10.0.100.92. We will include these IPs again later.

2. Add the IP address(es) where Tableau dashboard is going to be displayed. Open Command Prompt, then go to C:\Program Files (x86)\Tableau\Tableau Server\7.0\bin\ (location might vary), and use the command
tabadmin set wgserver.trusted_hosts "<Trusted IP Addresses>" 
to add the trusted hosts. Don't forget to also include the existing trusted IP addresses previously added, separated by comma if there is more than 1 IP address.
e.g. 
tabadmin set wgserver.trusted_hosts "10.0.0.91, 10.0.100.92, 10.0.0.99"

3. Save the configuration by using the command:
tabadmin config

4. Check the file dataserver.properties on step 1 and look for trusted_hosts. Now, the content of the trusted hosts should look like trusted_hosts=10.0.0.91, 10.0.100.92, 10.0.0.99.

5. Restart tableau server by using the command:
tabadmin restart
or run services.msc, then look for Tableau Server (tabsvc) service, and then restart the service.

6. Verify if the Tableau dashboard can be displayed properly (in this case, from 10.0.0.99).

7. That's all, folks!
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Report cannot be Displayed

Error:
- Event not fired.
- Microsoft.Reporting.WebForms.HttpHandlerInputException: Missing URL parameter: IterationId
(This is only part of the long error message).
- Report loads forever (never stops loading).

Solution:
On the aspx page, add attribute: EnableEventValidation="false"

For my particular case, I was trying to display a report (SSRS), and it never stopped loading. However, for my case, it was because of the version of the Internet Explorer (yes, the report is only compatible with IE for mine). After changing the version of the IE through developer tool (F12), I managed to display the report properly. You can also try to display the report from another machine using the intended IE version to see if it displays properly.
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Combine Rows into a Column

Happened to find a way to combine rows into a column. I find it quite useful, and it comes in handy.

For illustration, suppose we have UserGroup & Users. We want to list the users belonging to each group.

UserGroup:


Users:


If we do normal joining of the 2 tables, it will look like:


If we combine the values on the rows into a column, it will look like:


Here is the query to do so:

-- Create temporary table to store UserGroup
SELECT GroupID = 1, UserGroup = 'Group 1' INTO #UserGroup
INSERT INTO #UserGroup VALUES ( 2, 'Group 2' )
INSERT INTO #UserGroup VALUES ( 3, 'Group 3' )

-- Create temporary table to store Users
SELECT UserID = 'Superman', GroupID = 1 INTO #Users
INSERT INTO #Users VALUES ( 'Luck', 2 )
INSERT INTO #Users VALUES ( 'Himura', 1 )
INSERT INTO #Users VALUES ( 'Selvi', 1 )
INSERT INTO #Users VALUES ( 'Smarty', 2 )
INSERT INTO #Users VALUES ( 'Lucky', 3 )

-- Normal Join
SELECT a.UserGroup, b.UserID
FROM #UserGroup a
LEFT JOIN #Users b
 ON b.GroupID = a.GroupID
ORDER BY a.UserGroup

-- Combine Rows into Column
SELECT UserGroup, Users = STUFF(( SELECT ', ' + UserID FROM #Users a
    WHERE a.GroupID = b.GroupID
    ORDER BY a.UserID
    FOR XML PATH('') )
   , 1, 2, '')
FROM #UserGroup b
ORDER BY UserGroup

-- This is the key query to combine rows into column
SELECT UserID + ', ' FROM #Users
WHERE GroupID = 1
FOR XML PATH('')
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Mapping User Login and Database Roles to Existing User

Error:
User, group, or role 'xxx' already exists in the current database. (.Net SqlClient Data Provider)

Explanation:
This error happens when you try to add user mapping to the server logins using username which already exists in the database to be assigned.

In my case, the user exists in both server logins and database logins, but the user mapping and database roles on the server logins for this user cannot be modified although the user mapping is incorrect, because it already exists on the database logins.

Solution:
Run this script to update the user mapping accordingly.
USE <database_name>
EXEC sp_change_Users_login 'update_one', '<login_username>', '<login_username>'

This will update the user mapping and database roles on server logins to follow the ones on the database logins.
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Current Transaction Cannot be Committed

Error:
The current transaction cannot be committed and cannot support operations that write to the log file. Roll back the transaction.

This error occurs when you try to perform other operations when any transaction fails in try catch section, soon after it goes to catch section.

Solution:
You have to ROLLBACK first on the catch section before doing any other operations.
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