Accessing mysql database from oracle using dg4odbc

Question

I've been trying to create a database link from a MySQL database to Oracle using the Oracle dg4odbc gateway. I downloaded and installed DataDirect's ODBC package which includes mysql ODBC library (ddmysql24.so) and a generic ODBC libary (libodbc.so). After creating the DSN in odbc.ini, I tested it and it can connect to the mysql database. Then I created the init{SID}.ora file in hs/admin directory, added dg4odbc lines in the listener.ora, and added lines in tnsnames.ora. Then I tnspinged the new SID with success. Finally, I created the database link. However, when I tried to access the database link using the commands "select * from mdl_user@moodle;", I got the ORA-28500 error like the following:
ERROR at line 1:
ORA-28500: connection from ORACLE to a non-Oracle system returned this message:
[DataDirect][ODBC 20101 driver][20101]You have an error in your SQL syntax;
check the manual that corresponds to your MySQL server version for the right
syntax to use near '"mdl_user"' at line 1
ORA-02063: preceding 2 lines from MOODLE
My mysql database is utf8 by default. Do I have to use latin1?
It seems to me that the dg4odbc translates the sql commands incorrectly (having double quotes around the selected table).
Any help is greatly appreciated.
Jeffrey

Answer 1

The syntax error occures for example when MySQL isn't running in ANSI mode and thus does not allow double quotes around the objects. DG4ODBC 11.1.0.6 by default always adds double quotes to table/column/view names.
A quick test to check if you hit the double quote issue would be to set the MySQL DB into ANSI mode:
- Open SQL*Plus
- execute:
DECLARE
ret integer;
c integer;
BEGIN
c := DBMS_HS_PASSTHROUGH.OPEN_CURSOR@moodle;
DBMS_HS_PASSTHROUGH.PARSE@moodle(c, 'SET SESSION SQL_MODE=''ANSI_QUOTES'';');
ret := DBMS_HS_PASSTHROUGH.EXECUTE_NON_QUERY@moodle(c);
dbms_output.put_line(ret ||' passthrough output');
DBMS_HS_PASSTHROUGH.CLOSE_CURSOR@moodle(c);
END;
- Now run your select statement
=> if it now works, you can permanently change the MySQL config to be ANSI compliant or you can apply the 11.1.0.7 patchset to DG4ODBC.