I have two tables in my mySQL database:

我的mySQL数据库中有两个表：

table "animals":

表“动物”：

|   animal   |    name     | 
|:-----------|------------:|
|    cat     |     Tom     | 
|    dog     |             |   

table "orders":

表“订单”：

|     id     |   animal    | 
|:-----------|------------:|
|      1     |     cat     | 
|      2     |     dog     |  

At first I select from the table "orders" the following data:

首先，我从表中“选择”以下数据：

    <?php 
    $pdo = Database::connect();
    $sql = 'SELECT * FROM orders ORDER BY id ASC';
    foreach ($pdo->query($sql) as $row) {

    echo ('<td>a:'.$row['id'].'</td>');     
    echo ('<td>b:'.$row['animal'].'</td>'); 
    echo ('<td>c:'.$row['animal'].'</td>');         

    }
    Database::disconnect();
    ?>

Now I want to check if in my mySQL table "animal" the animal has a name. If yes print at position b the name. If there is no name print the animal:

现在我想检查一下我的mySQL表中的“动物”是否有动物的名字。如果是，则在位置b打印名称。如果没有名字打印动物：

|      a:1     |     b:Tom     |      c:cat     | 
|      a:2     |     b:dog     |      c:dog     | 

Thank you for your answers! I tried to work now with the answer of Jayo2k. I need to do a little change in my question, I found out I did a little mistake. So here I try to describe what I need as specific as possible:

谢谢您的回答！我现在尝试使用Jayo2k的答案。我需要对我的问题做一点改动，我发现我犯了一点错误。所以在这里我尝试尽可能具体地描述我需要的东西：

table "animals":

表“动物”：

|   name     |   animal    | 
|:-----------|------------:|
|    Tom     |     cat     | 
|   Jerry    |     dog     |   
|   Alfred   |    duck     |  
|    Sam     |             | 
|   Donald   |             |  

table "orders":

表“订单”：

|     id     |   animal    | 
|:-----------|------------:|
|      1     |     cat     | 
|      2     |     dog     |
|      3     |     duck    |
|      4     |     frog    |
|      5     |     pig     |

With the following code from Jayo2k...

使用Jayo2k的以下代码......

    <?php 
    $pdo = Database::connect();
    $sql = "SELECT * FROM animals, orders WHERE orders.animal = animals.animal";
    foreach ($pdo->query($sql) as $row) {

    echo '<tr> ';
    echo('<td>a:'.$row['id'].' </td>');
    echo('<td>a:'.$row['animal'].' </td>');
    echo('<td>b:'.$row['name'].' </td>');
    echo '</tr> ';

    }
    Database::disconnect();
    ?>      

... I get this result:

...我得到了这个结果：

|      a:1     |     b:cat     |      c:Tom     | 
|      a:2     |     b:dog     |      c:Jerry   |
|      a:3     |     b:duck    |      c:Alfred  |

But what I need is:

但我需要的是：

|      a:1     |     b:cat     |      c:Tom     | 
|      a:2     |     b:dog     |      c:Jerry   |
|      a:3     |     b:duck    |      c:Alfred  |
|      a:4     |     b:frog    |      c:frog    |
|      a:5     |     b:pig     |      c:pig     |

2 个解决方案

SELECT O.id, IF(IFNULL(A.name, '') = '', A.animal, A.name) name,  A.animal
FROM orders O
LEFT JOIN animals A 
    ON O.animal = A.animal
ORDER BY O.id DESC

SELECT * FROM animal, orders WHERE orders.animal = animals.animal

[0] =>
      id = 1
      name = tom
      animal = cat
[1] =>
      id = 2
      name = 
      animal = dog