odbc and mysql

[info]

Hi all,
Do you see why these lines are correct:

SQL1="select Id_Zone from zones  where ( Id_ref= '10' )",
{selected,Cols1,Rows1}=odbc:sql_query(Ref,SQL1),

But this one ...
{selected,["Id_Zone"],[{Idz}]=odbc:sql_query(Ref,SQL1),
... returns the following message:
Exception error: no match of right hand side value
{selected,["Id_Zone"],[{101}]

Are there restrictions with odbc ? columns syntax ? types of data ?