如何将在同一表上执行的两个 SQL 查询合并为一个？

Question

Below are the 2 queries I need to combine into one, and I like to have rows from the left table even if there is no matching row in the right table.

                    $sql = "SELECT country.printable_name FROM sku"
                    . "LEFT OUTER JOIN country ON country.numcode=sku.c_code"
                    . "WHERE sku.item_sku='JDJ2020'";

                   $sql= "SELECT hs_code FROM hs_codes"
                   . "INNER JOIN sku ON 
                   sku.base_category=hs_codes.base_category AND 
                   sku.sub_category=hs_codes.sub_category"
                   . "WHERE sku.item_sku = 'JDJ2020'";

Answer 1

After PHP code clearing the queries will look like

SELECT country.printable_name 
FROM sku
LEFT OUTER JOIN country ON country.numcode=sku.c_code
WHERE sku.item_sku='JDJ2020';

SELECT hs_code 
FROM hs_codes
INNER JOIN sku ON sku.base_category=hs_codes.base_category 
              AND sku.sub_category=hs_codes.sub_category
WHERE sku.item_sku = 'JDJ2020';

Their combining may look like

SELECT country.printable_name, hs_codes.hs_code
FROM sku
INNER JOIN hs_codes ON sku.base_category=hs_codes.base_category 
                   AND sku.sub_category=hs_codes.sub_category
LEFT OUTER JOIN country ON sku.c_code=country.numcode
WHERE sku.item_sku='JDJ2020';

If there exists a row in the country which matches the row in sku always then replace LEFT OUTER JOIN with INNER JOIN .

If there exists more than one matched row in country and/or hs_codes then you'll obtain more than one output row.