SQL查询返回0行

Question

SELECT * FROM class c 
Left join sub_inclass s on s.class_id=c.class_id 
join subject sb on  s.sub_id=sb.sub_id

除类“表”之外的其他两个为空，我已经退出联接，但类表仍未显示

Answer 1

如果仅使用join ，则默认情况下是inner join 。

SELECT * FROM class c 
Left join sub_inclass s on s.class_id=c.class_id 
left join subject sb on  s.sub_id=sb.sub_id
 ^-------------------you missed left here