Bootstrap 4 Cards of same height in columns

The Bootstrap 4 columns already use flexbox so they are the same height. Just use h-100 for height:100% on the cards and they'll fill the columns...

https://www.codeply.com/go/hKhPuxoovH

<div class="container">
    <div class="row">
            <div class="col-md-4 col-sm-6 col-12">
                <div class="card h-100">
                    <img src="images/dieux/Agni.jpg" alt="BeatsX">
                    <h1 class="card-title">BeatsX</h1>
                    <div class="text-center">
                        <p>1188.0000</p>
                        <p>2017-06-09 10:00:00</p>
                        <a href="god.php?ID=2" target="_blank" class="btn btn-primary">Voir la Fiche</a>
                    </div>
                </div>
            </div>
            <div class="col-md-4 col-sm-6 col-12">
                <div class="card h-100">
                    <img src="images/dieux/Agni.jpg" alt="Nitendo Switch">
                    <h1 class="card-title">Nitendo Switch</h1>
                    <div class="text-center">
                        <p>2899.0000</p>
                        <p>2017-06-10 10:00:00</p>
                        <a href="god.php?ID=3" target="_blank" class="btn btn-primary">Voir la Fiche</a>
                    </div>
                </div>
            </div>
            <div class="col-md-4 col-sm-6 col-12">
                <div class="card h-100">
                    <img src="images/dieux/Agni.jpg" alt="iPhone 7 128GB (Jet Blakc)">
                    <h1 class="card-title">iPhone 7 128GB (Jet Blakc)</h1>
                    <div class="text-center">
                        <p>6388.0000</p>
                        <p>2017-06-06 10:00:00</p>
                        <a href="god.php?ID=1" target="_blank" class="btn btn-primary">Voir la Fiche</a>
                    </div>
                </div>
            </div>
        </div>
</div>

Also there is no reason to float the cards, and the .col-* should be directly in the .row, not .card-deck

Use card-deck for equal size card this below code works for me

  <div class="card-deck">
    <div class="card mb-2">
        <img class="card-img-top img-fluid" src="//placehold.it/500x180" alt="Card image cap">
        <div class="card-body">
            <h4 class="card-title">Card title</h4>
            <p class="card-text">This is a wider card with supporting text below as a natural lead-in to additional content. This content is a little bit longer.</p>
            <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
        </div>
    </div>
    <div class="card mb-2">
        <img class="card-img-top img-fluid" src="//placehold.it/500x200" alt="Card image cap">
        <div class="card-body">
            <h4 class="card-title">Card title</h4>
            <p class="card-text">This card has supporting text below as a natural lead-in to additional content.This card has supporting text below as a natural lead-in to additional content.This card has supporting text below as a natural lead-in to additional content.</p>
            <p class="card-text"><small class="text-muted">Last updated 3 mins ago</small></p>
        </div>
    </div>
  </div>

Reference you can find here