mysql - MySQL Join 返回 Null

Question

我有两张桌子

Table_1
id|subject_code|subject_id
 1|Test1       |1
 2|Test2       |2
 3|Test3       |3

Table2
id|subject_id|grade|status
 1|1         |5.00 |Fail
 2|3         |2.25 |Pass

现在，我想创建一个返回以下内容的查询，

Table3
subject_code|grade|status
Test1       |5.00 |Fail
Test2       |NULL |NULL
Test3       |2.25 |Pass

我已经阅读了关于结合 left join 和 union all 但我不知道如何做到这一点。提前致谢。

Answer 1

尝试左连接，如下所示：

Select 
DISTINCT(table1.subject_code), 
grade, 
status

from table1 
LEFT join table2 on (table1.subject_id=table2.subject_id)

Answer 2

SELECT subject_code, grade, status 
FROM Table_1 t1 
LEFT JOIN Table2 t2 ON t1.subject_id = t2.subject_id;

Answer 3

我想一个简单的 LEFT JOIN 就可以了：

SELECT Table_1.subject_code, Table2.grade, Table2.status FROM Table_1 LEFT JOIN Table2 ON Table2.subject_id = Table_1.subject_id;