按条件分组连接两个表

Question

在这里，我想加入两个表并希望产生像

Akbar Travels building      2018-10
Thrikandiyur Quarters       2018-10


Akbar Travels building     2018-11
Thrikandiyur Quarters      2018-11

这里我有两个表名table A,table B，table A结构看起来像这样

category_id              category_name  
    5               Akbar Travels building          
    6               Thrikandiyur Quarters 

table B 结构看起来像这样

id     paying_month     parent_category     
1         2018-10           5   
2         2018-10           5   
3         2018-11           5   
4         2018-11           5   
5         2018-10           6   

在这里为了获得输出，我写了这样的代码

public function get_date_wise_pdf_report($from, $to)
{
       $query=$this->db->query("SELECT * from tableA A left join tableB B  on A.category_id = B.parent_category and B.paying_month BETWEEN '{$from}' AND '{$to}' ");
       return $query->result();
 }

但是当我使用它时，我变得像这样

Akbar Travels building     2018-10
Akbar Travels building     2018-10
Akbar Travels building     2018-11
Akbar Travels building     2018-11
Thrikandiyur Quarters      2018-10

我无法在这里给出 group by 语句，如果我只给出了两行，结果就会出来，请帮我解决

Answer 1

使用不同的

SELECT distinct A.category_name,B.paying_month
from tableA A left join tableB B  on A.category_id = B.parent_category and 
B.paying_month BETWEEN '{$from}' AND '{$to}'
order by B.paying_month