具有空白/空值的 MySQL JOIN 不返回任何结果

Question

我正在尝试可选地返回一些值（如果它们存在），如果不返回集合的其余部分。

SELECT people.first_name, countries1.name AS "Country1" 
FROM addressbook_people AS people
JOIN root_countries AS countries1 ON people.country1 = countries1.id

在某些情况下，不会为 people.country1 提供任何值，
但是，如果一个它没有提供任何结果。

我将如何重组此查询以仍然返回 people.first_name 当 people.country1 没有价值时？

Answer 1

做事

SELECT people.first_name, countries1.name AS "Country1" 
FROM addressbook_people AS people
LEFT JOIN root_countries AS countries1 ON people.country1 = countries1.id

这将导致在root_countries 表的各个字段上返回NULL。