Does Ms Access Support "Case When" Clause If Connect with Odbc

Does MS Access support CASE WHEN clause if connect with ODBC?

You could use IIF statement like in the next example:

SELECT
   IIF(test_expression, value_if_true, value_if_false) AS FIELD_NAME
FROM
   TABLE_NAME

What is the equivalent of Select Case in Access SQL?

Consider the Switch Function as an alternative to multiple IIf() expressions. It will return the value from the first expression/value pair where the expression evaluates as True, and ignore any remaining pairs. The concept is similar to the SELECT ... CASE approach you referenced but which is not available in Access SQL.

If you want to display a calculated field as commission:

SELECT
    Switch(
        OpeningBalance < 5001, 20,
        OpeningBalance < 10001, 30,
        OpeningBalance < 20001, 40,
        OpeningBalance >= 20001, 50
        ) AS commission
FROM YourTable;

If you want to store that calculated value to a field named commission:

UPDATE YourTable
SET commission =
    Switch(
        OpeningBalance < 5001, 20,
        OpeningBalance < 10001, 30,
        OpeningBalance < 20001, 40,
        OpeningBalance >= 20001, 50
        );

Either way, see whether you find Switch() easier to understand and manage. Multiple IIf()s can become mind-boggling as the number of conditions grows.

How to execute a pre-defined query having parameters (i.e. a PARAMETERS declaration) in a Microsoft Access database over ODBC?

When you're connecting over ODBC, look at the driver-specific information to see if it supports the various ODBC extensions (indicated by curly braces in the ODBC calls):

https://msdn.microsoft.com/en-us/library/ms675326(v=vs.85).aspx

Specifically:

ODBC provides a specific syntax for calling stored procedures. For the CommandText property of a Command object, the CommandText argument to the Execute method on a Connection object, or the Source argument to the Open method on a Recordset object, passes in a string with this syntax:

    "{ [ ? = ] call procedure [ ( ? [, ? [ , … ]] ) ] }"

Each ? references an object in the Parameters collection. The first ? references Parameters(0), the next ? references Parameters(1), and so on.
The parameter references are optional and depend on the structure of the stored procedure. If you want to call a stored procedure that defines no parameters, your string would look like the following:

    "{ call procedure }"

The Access ODBC driver exposes saved SELECT parameter queries as Stored Procedures, so that's why you use this syntax.

MS Access handle ODBC fault at opening database

When I will give the database to others, they will need to create this data source.

that is your first bad mistake and assumption. You MOST certainly do NOT want to deploy your applcation that way.

The way you deploy?

You take your accDB file, and link the tables to sql server. And you link using what is called DSN-less connections. Such connections do NOT require ANY data source to be setup on each work station.

So, ok, now you linked the tables to sql server (the production one - you probably were developing local on your developer PC and using a local copy of sql server express edition.

So, so now you link the tables to THEIR server, and then you now compile the accDB down to compiled executable version of Access - a accDE.

You are now free to deploy this "application" to any and all workstations for that company - and they do not have to re-link tables, do not have to setup a data source, and in fact they don't have to do anything, but simply run/launch the applcation.

How to make and get a dns-less connection?

Well, the MOST simple way is to ALWAYS, but ALWAYS ALWAYS create the linked tables using a FILE dsn. In fact, when you launch the ODBC connection manager from Access, the default is to use a FILE dsn. Never, and do not use "system" or "user" dsn.

If you link the tables using that FILE dsn, then Access converts them to DNS-less connections. At that point, you can even delete the DSN you created - access 100% ignores the DSN, and you don't need it anymore.

Next up:

If you been using nc 17 or nc 11-18 drivers? then yes, each workstation MUST have that same driver installed. Or, you can use the older "legacy" sql driver. But be careful - the legacy driver does not support datetime2 columns data types.

So, MAKE double, triple, quadrible sure that you not using data types and columns that require the newer drivers.

Right now, for some of the larger sites, we STILL use the older "legacy" driver, since that driver is installed at the OS level, and has been installed on every copy of windows going back to windows xp - in fact windows 98SE edition started shipping that driver. So you can 100% assume that the legacy sql driver is and will be installed on each workstation.

And by using + adopting dns-less connections, then no setup of the connection on each workstation is required. As long as those work stations are on the same network to sql server when YOU linked the tables, then they are good to go.

Now, on some sites, we actually can't even be on site, and we can't even pre-link to their sql server. So, what we do is on applcation startup, we check the current link for a linked table, and if it does not match a little external text file we ALSO included when setting up the work station, then we use VBA code to re-link the tables on startup. But once again, re-link of tables in VBA is easy, and again does NOT require ANY KIND of "dsn" or odbc setup on each work station.

And in fact, another way we used to do this is have a table in the front end, and it had one record, and that record had the connection string. So, right before deployment, we just edit that one record table in the front end to have the correct connection to their sql server. And once again, on startup , we check a linked table, and see if the connection strings match, if they don't, then we run the VBA re-link code, and once again, zero configuration and zero need exists to setup anything at all on each work station.

So, as a general rule, every dog, frog, insect that deployed access applications? We setup some re-link code and check that link on startup. In fact most developers have done this even without sql server - and even when using a access back end, then re-link code is included to resolve this issue.

but, be it linking to a access back end, or sql server back end? Some time of link check and system is assumed to have been cooked up by you, and this code will run on startup to check if the linked tables are pointing to the correct location.

But, be the back end oracle, sql server or whatever? You can create what is called dsn-less linked tables. As noted, you can use VBA to do this, or in fact you can use the linked table manager ---- as LONG AS you use a FILE dsn when you linked, then access coverts that to dns-less for you, and you be good to go.

so, in effect, you don't have to test/check/know for a odbc fail, since you checked the correct connection string on startup.

However, there is a way to trap, and check for a odbc failure, and this involves using a DIFFERENT way to connect, since we all know that if you have a odbc fail, you are duck soup (you have to exit Access, and there is NO KNOWN way around this issue - (well, except for testing if you can connect, and you do NOT use a linked table - since as noted once a odbc connect error triggers, it is game over.

The way you do this "alternate" test is like this:

Function TestLogin(strCon As String) As Boolean

  On Error GoTo TestError

  Dim dbs          As DAO.Database
  Dim qdf          As DAO.QueryDef

  Set dbs = CurrentDb()
  Set qdf = dbs.CreateQueryDef("")

   qdf.connect = strCon
   
   qdf.ReturnsRecords = False

   'Any VALID SQL statement that runs on server will work below.
   ' this does assume user has enough rights to query built in
   ' system tables
   
   qdf.sql = "SELECT 1 "
   qdf.Execute

   TestLogin = True
   
   Exit Function

TestError:
   TestLogin = False
   Exit Function

End Function

So, above does not hit or use a linked table. And a HUGE bonus of above? Once you execute that above valid logon, then any and all linked tables will work - AND WILL WORK without even having included the user/password in that connection string for the linked table. This is in have a huge bonus in terms of security, since now you don't have to include the user/password in the linked tables which of course exposes the user/password in plane text for all users that could look and see and find the sql user/password used.

In fact, what this means is that you can link your tables, but NOT include the user/password when you link the tables!!! - this is a HUGE security hole plugged and fixed when you do this.

So, once a valid logon has occurred (such as above), then any and all linked tables will now work, and work without even having included the user/passwords in those linked table connection strings.

As noted, the other big bonus is that you can use the above code to test for a valid connection, and avoid that dreaded "odbc" error, since as noted, if a odbc connection error is EVER triggered at any point in time, you MUST exit the applcation - no other way out.

However, it should be noted, that if you ever are going to use a wi-fi connection, or say cloud based sql server say running on Azure?

In that case, often with wi-fi, or a cloud based edition of sql server, then of course such connections over the internet are prone to minor and frequent dis-connects.

ODBC was developed long before the internet, and long before people would do things like connect access to some cloud based sql server running, and using a connection over the internet. But, if this turns out to be your use case, and deployment case?

Then you have to bite the bullet and ASSUME and ENSURE that you now adopt the nc 11-18 drivers. (I would go with nc17). These new drivers are now "internet" aware, and they are able to gracefully handle minor dis-conects, and in fact automatic re-cover and re-connect.

So, if you are ever going to use wi-fi, or connect to cloud based server? Then yes, you have to link the tables using say nc17 newer drivers, and you ALSO MUST THEN ensure that the same driver version you linked tables with is to be installed on each work station. You still don't have to setup any dsn connection and all that jazz - but you do have to ensure that the driver you used is ALSO installed on those work stations.

As noted, for larger deployments, we thus use the standard "legacy" sql driver, as it would be too painful to go to all work stations and install this driver.

However, we had one location, and for months they were experience in odbc connection failure. We had them replace a router, and even a network card on a server - but the problem still remained.

We suspect that some workstations had aggressive power management turned on, newer windows 10-11 will often put the network card to sleep, and thus when using access, we were seeing odbc errors. So, for that company, we had them install nc17, and linked access to sql server using that driver, and the problem went away (because those newer drivers now have built in re-connect ability - this is a relative new feature of ODBC, and one that legacy systems and drivers don't have.

Access warns that there is an operator error in the case clause in the query

There are actually 2 separate problems with that line.

1. Access has no CASE WHEN statements, and uses either the IIF function or SWITCH function instead
2. != is not a valid operator in Access. The not equals operator is <>.

Corrected:

IIF(Forms![g]![d] <> 0, z, Forms![g]![d]) AS EXP

How to check in Access VBA whether ODBC SQL Server table has write access?

You can use passthrough queries to get user role membership, and querydefs to create or access them:

Public Function is_datawriter() As Boolean
    Dim qdef As DAO.QueryDef
    Dim rst As DAO.Recordset

    Set qdef = CurrentDb.CreateQueryDef("")
    qdef.Connect = "ODBC; MY_ODBC_CONN_STRING"
    qdef.SQL = "SELECT IS_ROLEMEMBER('db_datawriter')"
    Set rst = qdef.OpenRecordset(dbOpenDynaset)
    If rst.Fields(0).Value = 1 Then is_datawriter = True
End Function

Testing table-specific rights is somewhat more difficult, but in your case this will probably do.

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