MySQL和PHP如果/不显示输出/回显[重复]

问题描述：

This question already has an answer here:

When to use single quotes, double quotes, and backticks in MySQL 12 answers

Alright so I am trying to make a page in my Admin control panel where you can view if the site is under some sort of maintenance. I am having trouble, not sure if it's from MySQL end, human error, or PHP.

Here is my code

<?php
$getMaint = mysql_query("SELECT * FROM 'system'");

      if($getMaint['maintenance'] == 1){ echo "<b align='center'>Maintenance is turned <j style='color:#00A808'>On</j></b>";
      }  else { echo "<b align='center'>Maintenance is turned <j align='center' style='color:#CC000A'>Off</j></b><br /><br />   "; }



    ?>

What I am getting on my end from it is either when having maintenance either 1 or 0 it shows Off no matter if in my database I change it from 0 or 1?

I am not sure if it's because the structure of maintenance number system is setup as a enum('0', '1')

What I want it to do is when maintenance is marked as 1 in database(MySQL) I want it to say On for maintenance or if 0 it will say Off.

---------------------------------Fixed---------------------------------------

My solution:

<?php
$getSystem = mysql_query("SELECT * FROM `system`");
while($Maint = mysql_fetch_array($getSystem))
{
      if($Maint['maintenance'] == 1){ echo "<b align='center'>Maintenance is turned <j style='color:#00A808'>On</j></b>";
      }  else { echo "<b align='center'>Maintenance is turned <j align='center' style='color:#CC000A'>Off</j></b><br /><br />   "; }
    }


    ?>

Thank you John Cone and juergen d

</div>

答

There are many issues with this code:

You use the deprecated mysql API which was removed in PHP 7. It should never be used anymore. You should be using mysqli or PDO. I'll use mysqli here since it's easier to continue to use your code as an example.
You use single quotes around your table name which is incorrect. You can use ticks or nothing.
You never fetch the results of your query
You don't check for errors. How do you know if anything went wrong, or what went wrong, if you don't bother to check?

<?php
$conn = mysqli_connect('localhost', 'my_user', 'my_password', 'my_db');
$result = mysqli_query($conn, "SELECT * FROM `system`");
if ($result) {
    $getMaint = mysqli_fetch_array($result);
    if($getMaint['maintenance'] == 1){ 
       echo "<b align='center'>Maintenance is turned <j style='color:#00A808'>On</j></b>";
    }  
    else { 
        echo "<b align='center'>Maintenance is turned <j align='center' style='color:#CC000A'>Off</j></b><br /><br />   "; 
    }
}
else {
    echo mysqli_ewrror($result);
}
?>

MySQL和PHP如果/不显示输出/回显[重复]

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