Relational model

<div class="demo"><div class="head"><b>JOIN ON customer_id</b><span id="pick">id 7</span></div><div class="stage join"><div class="table"><strong>orders</strong><div class="cell order">#51 → 7</div><div class="cell order">#52 → 9</div></div><div class="joinline" id="line">→</div><div class="table"><strong>customers</strong><div class="cell customer">7 · Mina</div><div class="cell customer">9 · Jun</div></div></div><div class="foot"><span id="result">#51 + Mina</span><span>matching keys</span></div></div>

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let n=0;function tick(){document.querySelectorAll('.order,.customer').forEach((e,i)=>e.classList.toggle('on',i%2===n));document.getElementById('pick').textContent='id '+(n?9:7);document.getElementById('result').textContent=n?'#52 + Jun':'#51 + Mina';n=1-n}tick();const t=setInterval(tick,1100);document.querySelector('.demo').onclick=()=>{clearInterval(t);tick()}