diff --git a/frontend/src/query-tool/style.css b/frontend/src/query-tool/style.css
index 017ca74..14df2d7 100644
--- a/frontend/src/query-tool/style.css
+++ b/frontend/src/query-tool/style.css
@@ -446,6 +446,134 @@ body {
   font-size: 13px;
 }
 
+/* ---- MultiSelect 元件 ---- */
+.multi-select {
+  position: relative;
+  min-width: 160px;
+}
+
+.multi-select-trigger {
+  width: 100%;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  padding: 8px 10px;
+  font-size: 13px;
+  color: #1f2937;
+  background: #ffffff;
+  cursor: pointer;
+}
+
+.multi-select-trigger:disabled {
+  cursor: not-allowed;
+  opacity: 0.7;
+}
+
+.multi-select-text {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+  text-align: left;
+}
+
+.multi-select-arrow {
+  color: #64748b;
+  font-size: 11px;
+}
+
+.multi-select-dropdown {
+  position: absolute;
+  top: calc(100% + 4px);
+  left: 0;
+  right: 0;
+  z-index: 20;
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  background: #ffffff;
+  box-shadow: 0 12px 24px rgba(15, 23, 42, 0.14);
+  overflow: hidden;
+}
+
+.multi-select-search {
+  display: block;
+  width: 100%;
+  border: none;
+  border-bottom: 1px solid var(--border);
+  padding: 8px 12px;
+  font-size: 13px;
+  color: #1f2937;
+  outline: none;
+  background: #f8fafc;
+}
+
+.multi-select-search::placeholder {
+  color: #94a3b8;
+}
+
+.multi-select-options {
+  max-height: 250px;
+  overflow-y: auto;
+  padding: 8px 0;
+}
+
+.multi-select-option {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+  width: 100%;
+  padding: 6px 12px;
+  border: none;
+  background: transparent;
+  font-size: 13px;
+  color: #334155;
+  cursor: pointer;
+  text-align: left;
+}
+
+.multi-select-option:hover {
+  background: #f8fafc;
+}
+
+.multi-select-option input[type='checkbox'] {
+  margin: 0;
+  width: 14px;
+  height: 14px;
+  accent-color: #2563eb;
+}
+
+.multi-select-empty {
+  padding: 12px;
+  text-align: center;
+  color: #94a3b8;
+  font-size: 13px;
+}
+
+.multi-select-actions {
+  display: flex;
+  gap: 8px;
+  padding: 8px 10px;
+  border-top: 1px solid var(--border);
+  background: #f8fafc;
+}
+
+.btn-sm {
+  padding: 4px 10px;
+  border: 1px solid var(--border);
+  border-radius: 6px;
+  background: #f8fafc;
+  color: var(--text);
+  cursor: pointer;
+  font-size: 12px;
+}
+
+.btn-sm:hover {
+  border-color: #c2d0e0;
+  background: #eef4fb;
+}
+
 /* ---- 表格高度變體 ---- */
 .query-tool-table-wrap.short {
   max-height: 360px;