这两天看到一张 sql join 图, 感觉非常直观. 在这里分享下

按照图片竖着的顺序写下每种 sql

• a left join b on a.key = b.key
• a left join b on a.key = b.key where b.key is null
• a full outer join b on a.key = b.key
• a. inner join b on a.key = b.key
• a full outer join b on a.key = b.key where a.key is null or b.key is null
• a right join b on a.key = b.key
• a right join b on a.key = b.key where a.key is null