Database normalization

<div class="demo"><div class="head"><b>NORMALIZE</b><span id="mode">before</span></div><div class="stage norm"><div class="records"><div class="cell">#51 · Mina</div><div class="cell">#52 · Mina</div></div><div class="split">→</div><div class="records"><div class="cell">customer 7 · Mina</div><div class="cell">orders 51, 52 → 7</div></div></div><div class="foot"><span id="note">name copied twice</span><span>one source of truth</span></div></div>

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let n=0;function tick(){document.querySelectorAll('.records').forEach((e,i)=>{e.style.opacity=i===n?'1':'.5';e.querySelectorAll('.cell').forEach(c=>c.classList.toggle('on',i===n))});document.getElementById('mode').textContent=n?'after':'before';document.getElementById('note').textContent=n?'customer updated once':'name copied twice';n=1-n}tick();const t=setInterval(tick,1200);document.querySelector('.demo').onclick=()=>{clearInterval(t);tick()}