Windows Server 2008 R2
IIS 7.5
.NET Framework 4

To analyze the bug I need some more information

• the DSN string
• ODBC trace log
• if possible definition of the table structure(s)

Thanks!

If you don't specify a character set in your DSN, utf8 as default is used.

Some query fails, since it contains a non latin1 character, e.g.

MariaDB [test]> set names utf8;

Query OK, 0 rows affected (0.01 sec)

MariaDB [test]> prepare my from "SELECT * FROM t1 WHERE a = 'я'";

ERROR 1267 (HY000): Illegal mix of collations (latin1_swedish_ci,IMPLICIT) and (utf8_general_ci,COERCIBLE) for operation '='

Either find the statement which contains an invalid latin1 character or use a different character set in your DSN:

CHARSET=latin1

The problem remains, without specifying character set on the DSN:

SELECT `value` FROM xmldata WHERE `key` = 'Key1'; <--- Returns OK

var cmd = new System.Data.Odbc.OdbcCommand("SELECT `value` FROM xmldata WHERE `key` = ?", conn);
cmd.Parameters.Add(new System.Data.Odbc.OdbcParameter("", "Key1"));
This one fails, no special characters from what I can see.

However, when specifying character set latin1, the latter does not fail but returns no rows.

Fixed in rev. 21

Looks like the issue is still there - I observed same error with ado using parameters. Taking it over for further investigation and fixing

Ok, looks like I reopened the bug a bit in hurry. Bug occurs if the field is different than the default charset used by the driver. But specifying CHARSET=<charset_used_in_db> perfectly cures the problem.
The testcase I used looks like this
Const DSN = "DSN=test"

Const adParamInput = &H0001

Const adCmdText = &H0001

Const adVarChar=200

Dim conn, rs, fld, cmd, pr

Set conn = CreateObject("ADODB.Connection")

conn.Open(DSN)

Set cmd = CreateObject("ADODB.Command")
cmd.ActiveConnection = conn
cmd.CommandText = "SELECT b FROM t WHERE a=?"
cmd.CommandType = adCmdText
Set pr = CreateObject("ADODB.Parameter")
'pr.Name = "a"
pr.Type = adVarChar
pr.Direction = adParamInput
pr.Size = 10
pr.Value = "фuu1"
cmd.Parameters.Append(pr)

Set rs = cmd.Execute()

Adding ;CHARSET=cp1251 to the connection string helped in my case(as the key field was in cp1251).
While checking the issue I stumbled upon ODBC-14 and fixed. Maybe it was real root of somebody's problems in similar scenario.