How can I connect a value of one mySQL table to a value of another table?

Question

I have two tables in my mySQL database:

table "animals":

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

table "orders":

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

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

    <?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:

|      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:

table "animals":

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

table "orders":

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

With the following code from Jayo2k...

    <?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:

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

But what I need is:

|      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     |

Answer 1

You can use LEFT JOIN, and use the IF condition to check the value is not empty, along with IFNULL, that will make null values in columns to blank.

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