exclude part of result

SELECT DISTINCT a, b, c, now(), count(item_pk) 
FROM product
LEFT JOIN item ON item.product_fk = product_pk
WHERE ...
GROUP BY a, b, c


I have another table 'navigation' which also has the columns a,b,c

If the combination of (a,b,c) exists in 'navigation', then exclude it
from above result. How can I achieve this?

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Best Regards,

Tarlika Elisabeth Schmitz


A: Because it breaks the logical sequence of discussion
Q: Why is top posting bad?