...

back-sql calls backsql_BindParamBerVal(), which indeed considers the data as SQL_C_CHAR, SQL_VARCHAR. A binary variant can be easily defined, but back-sql will need to know what attribute values need to be treated as binaries. A general approach to this requires to modify the attribute mapping, to add a "type" flag.

p.

I have carefully read the documentation (man slapd-sql) but could not find how to modify the attribute mapping and add a "type" flag.

I meant: modify the code. Since back-sql is basically unmaintained (any volunteers out there?) this feature won't likely be added, not to mention the fact that it would break all existing installations.

p.