如何合并两个表并将一个表的结果分组？

Question

I want to combine two tables.

table list :

| id   | day         | 
|:-----|------------:|
| 1    | monday      |   
|      |             |   
|      |             | 
|:-----|------------:| 
| 2    | tuesday     |   
|      |             |   

table animals :

| id   | animal      | list_id    |
|:-----|------------:|:----------:|
| 1    | cat         |      1     | 
|:-----|------------:|:----------:|  
| 2    | bird        |      1     | 
|:-----|------------:|:----------:| 
| 3    | monkey      |      1     | 
|:-----|------------:|:----------:| 
| 4    | frog        |      2     | 
|:-----|------------:|:----------:| 
| 5    | dog         |      2     | 
|:-----|------------:|:----------:| 

Here is my approach:

$animals = $db->query('SELECT *,
     GROUP_CONCAT(animals.animal SEPARATOR " <br> ") AS animals
     FROM list 
     LEFT JOIN animals ON list.id=animals.list_id
')->fetchAll(PDO::FETCH_ASSOC);

This is my desired result:

| id   | day         | animal       |
|:-----|------------:|:------------:|
| 1    | monday      |     cat      |    
|      |             |     bird     | 
|      |             |     monkey   |
|:-----|------------:|:------------:|  
| 2    | tuesday     |     frog    
|      |             |     dog     

But the result I actually get is:

| id   | day         | animal       |
|:-----|------------:|:------------:|
| 1    | monday      |     cat      |    
|      |             |     bird     | 
|      |             |     monkey   |
|      |             |     frog    
|      |             |     dog     

Answer 1

You want to merge all the animals with same list_id hence you need to use Group by with list_id . Group_concat() will concat all the results for each group. Hence, following query should work:

$animals = $db->query('SELECT l.*,
     GROUP_CONCAT(animals.animal SEPARATOR " <br> ") AS animals
     FROM list l
     LEFT JOIN animals ON list.id=animals.list_id
     group by animals.list_id    // Added statement
')->fetchAll(PDO::FETCH_ASSOC);

Hope it helps!