如何将在同一表上执行的两个 SQL 查询合并为一个？

Question

下面是我需要合并为一个的 2 个查询，即使右表中没有匹配的行，我也喜欢从左表中获取行。

                    $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

清除 PHP 代码后，查询将如下所示

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';

他们的组合可能看起来像

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';

如果存在一个排country该行匹配sku始终然后更换LEFT OUTER JOIN与INNER JOIN 。

如果country和/或hs_codes存在多个匹配行，那么您将获得多个输出行。