In this case I think it is better put condition into JOIN, than in WHERE.
SELECT marc_dummy~plifz ...
...
LEFT JOIN marc AS marc_dummy ON ( marc_dummy~matnr = marc~matnr AND
marc_dummy~werks = 'DM01 )
...
In this case I think it is better put condition into JOIN, than in WHERE.
SELECT marc_dummy~plifz ...
...
LEFT JOIN marc AS marc_dummy ON ( marc_dummy~matnr = marc~matnr AND
marc_dummy~werks = 'DM01 )
...