fix (sql compatibility): use sys_context to query tenant name on orac…

…le mode (#58)

flink-connector-oceanbase/src/main/java/com/oceanbase/connector/flink/dialect/OceanBaseOracleDialect.java

@@ -86,6 +86,6 @@ public String getSysDatabase() {
 
     @Override
     public String getQueryTenantNameStatement() {
-        return "SELECT TENANT_NAME FROM SYS.DBA_OB_TENANTS";
+        return "SELECT SYS_CONTEXT('USERENV', 'CON_NAME') FROM DUAL";
     }
 }