MBCS = multi byte character set. e.g. if you store a Korean string literal in an ANSI string, individual characters may use 2 or more bytes. The type of the field doesn't really matter as this query already fails during the parsing phase, long before it even gets to open the tables. MBCS strings shouldn't be any problem for the SQL engine as the engine itself is completely Unicode based. The SQL property of TnxQuery is a TStringList, so it stores MBCS ANSI strings in this case. But the string is passed as a WideString to the server and the compiler does create the required code to convert this MBCS ANSI string into a Unicode string.