PostgreSQL 18 can search a multicolumn B-tree using a later column without a leading equality condition.
<div class="demo"><div class="head"><b>INDEX (region, status)</b><span>WHERE status = open</span></div><div class="stage skips"><div class="group"><strong>A</strong><div class="cell hit">open</div><div class="cell">closed</div></div><div class="group"><strong>B</strong><div class="cell hit">open</div><div class="cell">closed</div></div><div class="group"><strong>C</strong><div class="cell hit">open</div><div class="cell">closed</div></div></div><div class="foot"><span id="skipstatus">seek A / open</span><span>skip to next prefix</span></div></div>*{box-sizing:border-box}.demo{width:min(96vw,820px);height:min(94vh,350px);padding:clamp(8px,2vmin,18px);border:1px solid var(--line);border-radius:14px;background:var(--surface);color:var(--fg);display:flex;flex-direction:column;gap:clamp(5px,1.5vmin,12px);font:600 clamp(12px,3.5vmin,15px)/1.25 var(--font-sans),sans-serif;overflow:hidden}.head,.foot,.row{display:flex;justify-content:space-between;align-items:center;gap:8px}.head b{color:var(--accent)}.head span,.foot,.muted{color:var(--muted)}.stage{flex:1;min-height:0;display:flex;align-items:center;justify-content:center;gap:8px}.cell,.pill{border:1px solid var(--line);border-radius:8px;background:var(--bg);padding:clamp(4px,1.2vmin,9px);text-align:center}.pill{border-radius:999px}.on{border-color:var(--accent)!important;background:color-mix(in srgb,var(--accent) 17%,var(--surface))!important;color:var(--fg)!important}.bad{border-color:#e16a5d!important;background:color-mix(in srgb,#e16a5d 18%,var(--surface))!important}.foot{font-size:clamp(12px,3vmin,14px)}.skips{justify-content:space-around}.group{display:grid;gap:5px;min-width:27%;text-align:center}.group strong{color:var(--muted)}.group .cell{padding:4px}.hit{transition:.3s}@media(max-width:400px){.skips{gap:3px}.group{min-width:30%}}let n=0;function tick(){document.querySelectorAll('.hit').forEach((e,i)=>e.classList.toggle('on',i===n));document.getElementById('skipstatus').textContent='seek '+['A','B','C'][n]+' / open';n=(n+1)%3}tick();const t=setInterval(tick,1100);document.querySelector('.demo').onclick=()=>{clearInterval(t);tick()}Column order matters in a multicolumn B-tree index. PostgreSQL 18 skip scan can repeatedly search the index using a later-column condition even without equality on a leading column.
The demo visits regions A, B, and C and selects keys with status=open. The planner does not always choose this path; distribution and cost may favor a full scan.
Check the plan for queries that filter only later columns of a multicolumn index.