Foreach循环：如果字符串等于前一个字符串

So, I am creating a history of changes page from database that has one row for each update. I need to represent only values that have changed. I represent those values in foreach loop (to make it more simple I reduced it to 1 value: work stations):

$sth = $pdo->prepare("
SELECT * FROM user_customers_history
");

$sth->execute();

foreach ($sth as $key => $row) {

$crm_workstations = $row['crm_workstations'];

if (($crm_workstations > 0) && ($crm_workstations != $crm_workstations)){

        echo '<br/><br/>' . $crm_workstations;

}

I defined $key as an index, but I don't know how to use it. I know that I want to represent it this way: for each index check if the value is equal to previous index value. If they are not equal, show it.

Define a previous value for your variable to compare with the current one:

$sth = $pdo->prepare("
SELECT * FROM user_customers_history
");

$sth->execute();

$prev_workstations = '';

while ($row = $sth->fetch()) { 

    $crm_workstations = $row['crm_workstations'];
    if (($crm_workstations > 0) && ($crm_workstations != $prev_workstations)){

        $prev_workstations = $crm_workstations;
        echo '<br/><br/>' . $crm_workstations;

    }  
}

They ask me to edit more then 6 characters I needed to write somthing :D