Say I have DAILY_SALES and DAILY_INVENTORY data tables. If I use LEFT JOIN on both tables (for SSR measurement) only with <=> operator and group-by, the result is correct. If I have sales data but not inventory on certain date, it will return NULL.

However, if I have DAILY_SALES_SUMMARY (query table of DAILY_SALES) and DAILY_INVENTORY_SUMMARY (query table of DAILY_INVETORY) then I make another query table say SSR2 querying both query tables, with the same method using LEFT JOIN and <=> operator, the result is wrong. The LEFT JOIN resulting like inner JOIN.