diff --git a/src/components/grid/DataGrid.vue b/src/components/grid/DataGrid.vue
index 3d0f9da3f..c25f883fe 100644
--- a/src/components/grid/DataGrid.vue
+++ b/src/components/grid/DataGrid.vue
@@ -7,7 +7,7 @@ const globalDdlOpen = ref(false);
 import { computed, nextTick, onUnmounted, watch } from "vue";
 import { useElementSize } from "@vueuse/core";
 import { useI18n } from "vue-i18n";
-import { ArrowUp, ArrowDown, Download, Plus, Trash2, Save, ChevronLeft, ChevronRight, Search, Inbox, SearchX, Code2, Copy, Loader2, X, Undo2, WrapText } from "lucide-vue-next";
+import { ArrowUp, ArrowDown, Download, Plus, Trash2, Save, ChevronLeft, ChevronRight, Search, Inbox, SearchX, Code2, Copy, Loader2, X, Undo2, WrapText, Info } from "lucide-vue-next";
 import { Button } from "@/components/ui/button";
 import { Badge } from "@/components/ui/badge";
 import {
@@ -23,6 +23,17 @@ import type { QueryResult, ColumnInfo, DatabaseType } from "@/types/database";
 import { save as savePath } from "@tauri-apps/plugin-dialog";
 import { writeTextFile } from "@tauri-apps/plugin-fs";
 import * as api from "@/lib/tauri";
+import {
+  extractSelection,
+  formatSelectionAsCsv,
+  formatSelectionAsJson,
+  formatSelectionAsSqlInList,
+  formatSelectionAsTsv,
+  isCellInSelection,
+  normalizeSelectionRange,
+  type CellPosition,
+  type CellSelectionRange,
+} from "@/lib/gridSelection";
 
 import { useToast } from "@/composables/useToast";
 
@@ -102,7 +113,12 @@ function typeColorClass(t: string): string {
   if (["bytea", "blob", "binary", "varbinary", "image"].includes(s)) return "text-red-400";
   return "text-muted-foreground";
 }
-const contextCell = ref<{ rowId: number; col: number } | null>(null);
+const contextCell = ref<{ rowId: number; rowIndex: number; col: number } | null>(null);
+const selectionAnchor = ref<CellPosition | null>(null);
+const selectionFocus = ref<CellPosition | null>(null);
+const isSelectingCells = ref(false);
+const detailCell = ref<{ rowIndex: number; col: number } | null>(null);
+const showCellDetail = ref(false);
 const sortCol = ref<string | null>(null);
 const sortDir = ref<"asc" | "desc">("asc");
 const searchText = ref("");
@@ -257,6 +273,46 @@ const displayItems = computed<RowItem[]>(() => {
 const hasVisibleRows = computed(() => displayItems.value.length > 0);
 const emptyTitle = computed(() => searchText.value ? t('grid.noSearchResults') : t('grid.noRows'));
 const emptyDescription = computed(() => searchText.value ? t('grid.noSearchResultsDescription') : t('grid.noRowsDescription'));
+const selectedRange = computed<CellSelectionRange | null>(() => {
+  if (!selectionAnchor.value || !selectionFocus.value) return null;
+  return normalizeSelectionRange(selectionAnchor.value, selectionFocus.value);
+});
+const visibleSelectionRows = computed(() => displayItems.value.map((item) => item.data));
+const selectedCells = computed(() => extractSelection(props.result.columns, visibleSelectionRows.value, selectedRange.value));
+const selectedCellCount = computed(() => selectedCells.value.columns.length * selectedCells.value.rows.length);
+const hasCellSelection = computed(() => selectedCellCount.value > 0);
+const selectionSummary = computed(() => t("grid.selectedCells", { count: selectedCellCount.value }));
+const activeCellDetail = computed(() => {
+  const cell = detailCell.value;
+  if (!cell) return null;
+  const item = displayItems.value[cell.rowIndex];
+  const column = props.result.columns[cell.col];
+  if (!item || !column) return null;
+  const value = item.data[cell.col] ?? null;
+  const rawValue = formatCell(value);
+  const valueText = value === null ? "" : String(value);
+  const trimmed = valueText.trim();
+  const maybeJson = typeof value === "string" && (trimmed.startsWith("{") || trimmed.startsWith("["));
+  let formattedJson = "";
+  if (maybeJson) {
+    try {
+      formattedJson = JSON.stringify(JSON.parse(value), null, 2);
+    } catch {
+      formattedJson = "";
+    }
+  }
+  return {
+    rowNumber: cell.rowIndex + 1,
+    colIndex: cell.col,
+    column,
+    type: columnTypeMap.value.get(column) || "",
+    comment: columnCommentMap.value.get(column) || "",
+    value,
+    rawValue,
+    length: value === null ? 0 : String(value).length,
+    formattedJson,
+  };
+});
 
 function toggleSort(colName: string) {
   if (isResizing) return;
@@ -574,16 +630,111 @@ function discardChanges() {
   editingCell.value = null;
 }
 
+// --- Cell selection and detail ---
+function clearCellSelection() {
+  selectionAnchor.value = null;
+  selectionFocus.value = null;
+  isSelectingCells.value = false;
+}
+
+function selectSingleCell(rowIndex: number, colIndex: number) {
+  const cell = { rowIndex, colIndex };
+  selectionAnchor.value = cell;
+  selectionFocus.value = cell;
+}
+
+function finishCellSelection() {
+  isSelectingCells.value = false;
+  document.removeEventListener("mouseup", finishCellSelection);
+}
+
+function beginCellSelection(rowIndex: number, colIndex: number, event: MouseEvent) {
+  if (event.button !== 0) return;
+  if (editingCell.value) return;
+  event.preventDefault();
+  selectSingleCell(rowIndex, colIndex);
+  isSelectingCells.value = true;
+  document.addEventListener("mouseup", finishCellSelection);
+}
+
+function extendCellSelection(rowIndex: number, colIndex: number) {
+  if (!isSelectingCells.value || !selectionAnchor.value) return;
+  selectionFocus.value = { rowIndex, colIndex };
+}
+
+function cellIsSelected(rowIndex: number, colIndex: number): boolean {
+  return isCellInSelection(rowIndex, colIndex, selectedRange.value);
+}
+
+function showCellDetails(rowIndex: number, colIndex: number) {
+  detailCell.value = { rowIndex, col: colIndex };
+  showCellDetail.value = true;
+}
+
+function copyText(text: string) {
+  navigator.clipboard.writeText(text);
+  toast(t('grid.copied'));
+}
+
+function copySelectionTsv() {
+  if (!hasCellSelection.value) return;
+  copyText(formatSelectionAsTsv(selectedCells.value));
+}
+
+function copySelectionCsv() {
+  if (!hasCellSelection.value) return;
+  copyText(formatSelectionAsCsv(selectedCells.value));
+}
+
+function copySelectionJson() {
+  if (!hasCellSelection.value) return;
+  copyText(formatSelectionAsJson(selectedCells.value));
+}
+
+function copySelectionSqlInList() {
+  if (!hasCellSelection.value) return;
+  copyText(formatSelectionAsSqlInList(selectedCells.value));
+}
+
+function copyDetailValue() {
+  if (!activeCellDetail.value) return;
+  copyText(activeCellDetail.value.rawValue);
+}
+
+function copyDetailColumnName() {
+  if (!activeCellDetail.value) return;
+  copyText(activeCellDetail.value.column);
+}
+
+function copyDetailSqlCondition() {
+  const detail = activeCellDetail.value;
+  if (!detail) return;
+  const column = quoteIdent(detail.column);
+  const condition = detail.value === null
+    ? `${column} IS NULL`
+    : `${column} = ${escapeVal(detail.value)}`;
+  copyText(condition);
+}
+
+watch(() => props.result, () => {
+  clearCellSelection();
+  showCellDetail.value = false;
+  detailCell.value = null;
+});
+
 // --- Copy/Export ---
-function onCellContext(rowId: number, colIdx: number) {
-  contextCell.value = { rowId, col: colIdx };
+function onCellContext(rowId: number, rowIndex: number, colIdx: number) {
+  contextCell.value = { rowId, rowIndex, col: colIdx };
+  if (!cellIsSelected(rowIndex, colIdx)) {
+    selectSingleCell(rowIndex, colIdx);
+  }
 }
 
 function copyCell() {
   if (!contextCell.value) return;
   const item = getRowItem(contextCell.value.rowId);
   const val = item?.data[contextCell.value.col] ?? null;
-  navigator.clipboard.writeText(formatCell(val));
+  copyText(formatCell(val));
 }
 
 function copyRow() {
@@ -592,7 +743,7 @@ function copyRow() {
   if (!item) return;
   const obj: Record<string, unknown> = {};
   props.result.columns.forEach((col, i) => { obj[col] = item.data[i]; });
-  navigator.clipboard.writeText(JSON.stringify(obj, null, 2));
+  copyText(JSON.stringify(obj, null, 2));
 }
 
 function copyAll() {
@@ -600,7 +751,7 @@ function copyAll() {
   const body = sortedRows.value
     .map(({ row, sourceIndex }) => rowDataWithChanges(row, sourceIndex).map((c) => formatCell(c)).join("\t"))
     .join("\n");
-  navigator.clipboard.writeText(`${header}\n${body}`);
+  copyText(`${header}\n${body}`);
 }
 
 async function exportCsv() {
@@ -721,7 +872,10 @@ function onDdlResizeEnd() {
   window.removeEventListener("mouseup", onDdlResizeEnd);
 }
 
-onUnmounted(onDdlResizeEnd);
+onUnmounted(() => {
+  onDdlResizeEnd();
+  finishCellSelection();
+});
 
 const SQL_KEYWORDS = /\b(CREATE|TABLE|INDEX|UNIQUE|PRIMARY|KEY|FOREIGN|REFERENCES|CONSTRAINT|NOT|NULL|DEFAULT|INT|INTEGER|BIGINT|SMALLINT|VARCHAR|CHARACTER|VARYING|TEXT|BOOLEAN|DOUBLE|PRECISION|REAL|FLOAT|NUMERIC|DECIMAL|TIMESTAMP|DATE|TIME|SERIAL|AUTOINCREMENT|AUTO_INCREMENT|IF|EXISTS|ON|SET|CASCADE|RESTRICT|CHECK|WITH|WITHOUT|ZONE)\b/gi;
 
@@ -879,17 +1033,20 @@ function escapeAndHighlightKeywords(s: string): string {
                 <div
                   v-for="(cell, colIdx) in item.data"
                   :key="colIdx"
-                  class="shrink-0 px-3 py-1 border-r border-border whitespace-nowrap overflow-hidden text-ellipsis relative"
+                  class="group/cell shrink-0 px-3 py-1 border-r border-border whitespace-nowrap overflow-hidden text-ellipsis relative select-none"
                   :style="{ width: `var(--col-w-${colIdx})` }"
                   :class="{
                     'text-muted-foreground italic': isNull(cell),
                     'bg-yellow-500/10': item.isDirtyCol[colIdx],
+                    'cell-selected': cellIsSelected(index, colIdx),
                     'tabular-nums': typeof cell === 'number',
                     'cursor-text hover:bg-accent/50': editable && !item.isDeleted,
                     'line-through': item.isDeleted,
                   }"
+                  @mousedown="beginCellSelection(index, colIdx, $event)"
+                  @mouseenter="extendCellSelection(index, colIdx)"
                   @dblclick="editable && !item.isDeleted && startEdit(item.id, colIdx)"
-                  @contextmenu="onCellContext(item.id, colIdx)"
+                  @contextmenu="onCellContext(item.id, index, colIdx)"
                 >
                   <template v-if="editingCell?.rowId === item.id && editingCell?.col === colIdx">
                     <input
@@ -902,6 +1059,14 @@ function escapeAndHighlightKeywords(s: string): string {
                   </template>
                   <template v-else>
                     {{ formatCell(cell) }}
+                    <button
+                      class="absolute right-0.5 top-0.5 hidden h-5 w-5 items-center justify-center rounded bg-background/90 text-muted-foreground shadow-sm ring-1 ring-border hover:text-foreground group-hover/cell:flex"
+                      :title="t('grid.cellDetails')"
+                      @mousedown.stop
+                      @click.stop="showCellDetails(index, colIdx)"
+                    >
+                      <Info class="h-3 w-3" />
+                    </button>
                   </template>
                 </div>
               </div>
@@ -942,15 +1107,87 @@ function escapeAndHighlightKeywords(s: string): string {
                 v-html="highlightSql(ddlContent)"
               ></pre>
             </div>
+            <!-- Cell Detail Drawer -->
+            <div
+              v-if="showCellDetail && activeCellDetail"
+              class="relative w-80 shrink-0 border-l flex flex-col bg-background min-w-0"
+            >
+              <div class="flex items-center gap-2 px-3 py-1.5 border-b shrink-0 bg-muted/20">
+                <Info class="w-3.5 h-3.5 text-muted-foreground" />
+                <span class="text-xs font-medium flex-1 min-w-0 truncate">{{ t('grid.cellDetails') }}</span>
+                <Button variant="ghost" size="icon" class="h-5 w-5" @click="showCellDetail = false">
+                  <X class="w-3 h-3" />
+                </Button>
+              </div>
+
+              <div class="flex-1 min-h-0 overflow-auto p-3 text-xs space-y-3">
+                <div class="space-y-1">
+                  <div class="text-muted-foreground">{{ t('grid.columnName') }}</div>
+                  <div class="font-medium break-all">{{ activeCellDetail.column }}</div>
+                </div>
+                <div class="grid grid-cols-2 gap-3">
+                  <div class="space-y-1">
+                    <div class="text-muted-foreground">{{ t('grid.rowNumber') }}</div>
+                    <div>{{ activeCellDetail.rowNumber }}</div>
+                  </div>
+                  <div class="space-y-1">
+                    <div class="text-muted-foreground">{{ t('grid.columnType') }}</div>
+                    <div :class="activeCellDetail.type ? typeColorClass(activeCellDetail.type) : 'text-muted-foreground'">
+                      {{ activeCellDetail.type || '-' }}
+                    </div>
+                  </div>
+                  <div class="space-y-1">
+                    <div class="text-muted-foreground">{{ t('grid.nullValue') }}</div>
+                    <div>{{ activeCellDetail.value === null ? 'true' : 'false' }}</div>
+                  </div>
+                  <div class="space-y-1">
+                    <div class="text-muted-foreground">{{ t('grid.valueLength') }}</div>
+                    <div>{{ activeCellDetail.length }}</div>
+                  </div>
+                </div>
+                <div class="space-y-1">
+                  <div class="text-muted-foreground">{{ t('grid.columnComment') }}</div>
+                  <div class="whitespace-pre-wrap break-words">{{ activeCellDetail.comment || t('grid.noComment') }}</div>
+                </div>
+                <div class="space-y-1">
+                  <div class="text-muted-foreground">{{ t('grid.cellValue') }}</div>
+                  <pre class="max-h-56 overflow-auto rounded border bg-muted/20 p-2 font-mono text-xs whitespace-pre-wrap break-words">{{ activeCellDetail.rawValue }}</pre>
+                </div>
+                <div v-if="activeCellDetail.formattedJson" class="space-y-1">
+                  <div class="text-muted-foreground">{{ t('grid.formattedJson') }}</div>
+                  <pre class="max-h-72 overflow-auto rounded border bg-muted/20 p-2 font-mono text-xs whitespace-pre-wrap break-words">{{ activeCellDetail.formattedJson }}</pre>
+                </div>
+              </div>
+
+              <div class="border-t p-2 grid grid-cols-1 gap-1">
+                <Button variant="ghost" size="sm" class="h-7 justify-start text-xs" @click="copyDetailValue">
+                  <Copy class="w-3 h-3 mr-2" /> {{ t('grid.copyValue') }}
+                </Button>
+                <Button variant="ghost" size="sm" class="h-7 justify-start text-xs" @click="copyDetailColumnName">
+                  <Copy class="w-3 h-3 mr-2" /> {{ t('grid.copyColumnName') }}
+                </Button>
+                <Button variant="ghost" size="sm" class="h-7 justify-start text-xs" @click="copyDetailSqlCondition">
+                  <Code2 class="w-3 h-3 mr-2" /> {{ t('grid.copySqlCondition') }}
+                </Button>
+              </div>
+            </div>
           </div>
         </div>
       </ContextMenuTrigger>
 
-      <ContextMenuContent class="w-48">
+      <ContextMenuContent class="w-60">
         <ContextMenuItem @click="copyCell">{{ t('grid.copyCell') }}</ContextMenuItem>
         <ContextMenuItem @click="copyRow">{{ t('grid.copyRow') }}</ContextMenuItem>
         <ContextMenuItem @click="copyAll">{{ t('grid.copyAll') }}</ContextMenuItem>
         <ContextMenuSeparator />
+        <template v-if="hasCellSelection">
+          <ContextMenuItem @click="copySelectionTsv">{{ t('grid.copySelectionTsv') }}</ContextMenuItem>
+          <ContextMenuItem @click="copySelectionCsv">{{ t('grid.copySelectionCsv') }}</ContextMenuItem>
+          <ContextMenuItem @click="copySelectionJson">{{ t('grid.copySelectionJson') }}</ContextMenuItem>
+          <ContextMenuItem @click="copySelectionSqlInList">{{ t('grid.copySelectionSql') }}</ContextMenuItem>
+          <ContextMenuItem @click="clearCellSelection">{{ t('grid.clearSelection') }}</ContextMenuItem>
+          <ContextMenuSeparator />
+        </template>
         <template v-if="editable">
           <ContextMenuItem class="text-destructive" @click="deleteSelectedRow">
             <Trash2 class="w-3.5 h-3.5 mr-2" /> {{ t('grid.deleteRow') }}
@@ -978,6 +1215,7 @@ function escapeAndHighlightKeywords(s: string): string {
       <span v-if="hasData">{{ t('grid.rows', { count: result.rows.length }) }}</span>
       <span v-else>{{ t('grid.rowsAffected', { count: result.affected_rows }) }}</span>
       <span>{{ result.execution_time_ms }}ms</span>
+      <span v-if="hasCellSelection" class="text-foreground">{{ selectionSummary }}</span>
 
       <template v-if="editable && tableMeta">
         <span v-if="hasPendingChanges" class="ml-2 text-foreground">
@@ -1065,6 +1303,11 @@ function escapeAndHighlightKeywords(s: string): string {
   transition: none;
 }
 
+.cell-selected {
+  background-color: color-mix(in oklab, var(--primary) 18%, transparent);
+  box-shadow: inset 0 0 0 1px color-mix(in oklab, var(--primary) 55%, transparent);
+}
+
 .ddl-code :deep(.ddl-kw) {
   color: oklch(0.6 0.15 250);
   font-weight: 600;
diff --git a/src/i18n/locales/en.ts b/src/i18n/locales/en.ts
index bd9c9847d..4181af485 100644
--- a/src/i18n/locales/en.ts
+++ b/src/i18n/locales/en.ts
@@ -86,6 +86,11 @@ export default {
     copyCell: "Copy Cell",
     copyRow: "Copy Row (JSON)",
     copyAll: "Copy All (TSV)",
+    copySelectionTsv: "Copy Selection (TSV)",
+    copySelectionCsv: "Copy Selection (CSV)",
+    copySelectionJson: "Copy Selection (JSON)",
+    copySelectionSql: "Copy Selection as SQL IN List",
+    clearSelection: "Clear Selection",
     exportCsv: "Export CSV",
     exportJson: "Export JSON",
     exportMarkdown: "Export Markdown",
@@ -105,6 +110,20 @@ export default {
     statusEdited: "Edited",
     statusDeleted: "Deleted",
     pendingChanges: "{count} pending",
+    selectedCells: "{count} selected",
+    cellDetails: "Cell Details",
+    cellValue: "Value",
+    columnName: "Column",
+    columnType: "Type",
+    columnComment: "Comment",
+    rowNumber: "Row",
+    valueLength: "Length",
+    nullValue: "NULL",
+    noComment: "No comment",
+    formattedJson: "Formatted JSON",
+    copyValue: "Copy Value",
+    copyColumnName: "Copy Column Name",
+    copySqlCondition: "Copy SQL Condition",
     rowsPerPageShort: " rows",
   },
   welcome: {
diff --git a/src/i18n/locales/zh-CN.ts b/src/i18n/locales/zh-CN.ts
index c8c764385..51e5ffe8b 100644
--- a/src/i18n/locales/zh-CN.ts
+++ b/src/i18n/locales/zh-CN.ts
@@ -88,6 +88,11 @@ export default {
     copyCell: "复制单元格",
     copyRow: "复制行 (JSON)",
     copyAll: "复制全部 (TSV)",
+    copySelectionTsv: "复制选区 (TSV)",
+    copySelectionCsv: "复制选区 (CSV)",
+    copySelectionJson: "复制选区 (JSON)",
+    copySelectionSql: "复制选区为 SQL IN 列表",
+    clearSelection: "清除选区",
     exportCsv: "导出 CSV",
     exportJson: "导出 JSON",
     exportMarkdown: "导出 Markdown",
@@ -107,6 +112,20 @@ export default {
     statusEdited: "已改",
     statusDeleted: "删除",
     pendingChanges: "{count} 项待保存",
+    selectedCells: "已选 {count} 个单元格",
+    cellDetails: "单元格详情",
+    cellValue: "值",
+    columnName: "列名",
+    columnType: "类型",
+    columnComment: "注释",
+    rowNumber: "行号",
+    valueLength: "长度",
+    nullValue: "NULL",
+    noComment: "暂无注释",
+    formattedJson: "格式化 JSON",
+    copyValue: "复制值",
+    copyColumnName: "复制列名",
+    copySqlCondition: "复制 SQL 条件",
     rowsPerPageShort: " 行/页",
   },
   welcome: {
diff --git a/src/lib/gridSelection.ts b/src/lib/gridSelection.ts
new file mode 100644
index 000000000..758557df5
--- /dev/null
+++ b/src/lib/gridSelection.ts
@@ -0,0 +1,102 @@
+export type GridCellValue = string | number | boolean | null;
+
+export interface CellPosition {
+  rowIndex: number;
+  colIndex: number;
+}
+
+export interface CellSelectionRange {
+  startRow: number;
+  endRow: number;
+  startCol: number;
+  endCol: number;
+}
+
+export interface SelectionData {
+  columns: string[];
+  rows: GridCellValue[][];
+}
+
+export function normalizeSelectionRange(anchor: CellPosition, focus: CellPosition): CellSelectionRange {
+  return {
+    startRow: Math.min(anchor.rowIndex, focus.rowIndex),
+    endRow: Math.max(anchor.rowIndex, focus.rowIndex),
+    startCol: Math.min(anchor.colIndex, focus.colIndex),
+    endCol: Math.max(anchor.colIndex, focus.colIndex),
+  };
+}
+
+export function isCellInSelection(rowIndex: number, colIndex: number, range: CellSelectionRange | null): boolean {
+  if (!range) return false;
+  return (
+    rowIndex >= range.startRow
+    && rowIndex <= range.endRow
+    && colIndex >= range.startCol
+    && colIndex <= range.endCol
+  );
+}
+
+export function extractSelection(
+  columns: readonly string[],
+  rows: readonly GridCellValue[][],
+  range: CellSelectionRange | null,
+): SelectionData {
+  if (!range) return { columns: [], rows: [] };
+
+  const selectedColumns = columns.slice(range.startCol, range.endCol + 1);
+  const selectedRows = rows
+    .slice(range.startRow, range.endRow + 1)
+    .map((row) => row.slice(range.startCol, range.endCol + 1));
+
+  return { columns: selectedColumns, rows: selectedRows };
+}
+
+function displayValue(value: GridCellValue): string {
+  if (value === null) return "NULL";
+  if (typeof value === "boolean") return value ? "true" : "false";
+  return String(value);
+}
+
+function csvValue(value: GridCellValue | string): string {
+  const text = typeof value === "string" ? value : displayValue(value);
+  return `"${text.replace(/"/g, '""')}"`;
+}
+
+function sqlValue(value: GridCellValue): string {
+  if (value === null) return "NULL";
+  if (typeof value === "boolean") return value ? "TRUE" : "FALSE";
+  if (typeof value === "number" && Number.isFinite(value)) return String(value);
+  return `'${String(value).replace(/'/g, "''")}'`;
+}
+
+export function formatSelectionAsTsv(selection: SelectionData): string {
+  const header = selection.columns.join("\t");
+  const body = selection.rows
+    .map((row) => row.map(displayValue).join("\t"))
+    .join("\n");
+  return [header, body].filter(Boolean).join("\n");
+}
+
+export function formatSelectionAsCsv(selection: SelectionData): string {
+  const header = selection.columns.map(csvValue).join(",");
+  const body = selection.rows
+    .map((row) => row.map(csvValue).join(","))
+    .join("\n");
+  return [header, body].filter(Boolean).join("\n");
+}
+
+export function formatSelectionAsJson(selection: SelectionData): string {
+  const objects = selection.rows.map((row) => {
+    const item: Record<string, GridCellValue> = {};
+    selection.columns.forEach((column, index) => {
+      item[column] = row[index] ?? null;
+    });
+    return item;
+  });
+  return JSON.stringify(objects, null, 2);
+}
+
+export function formatSelectionAsSqlInList(selection: SelectionData): string {
+  const values = selection.rows.flat().map(sqlValue);
+  return `(${values.join(", ")})`;
+}
diff --git a/tests/gridSelection.test.ts b/tests/gridSelection.test.ts
new file mode 100644
index 000000000..9523d9e13
--- /dev/null
+++ b/tests/gridSelection.test.ts
@@ -0,0 +1,68 @@
+import { strict as assert } from "node:assert";
+import test from "node:test";
+import {
+  extractSelection,
+  formatSelectionAsCsv,
+  formatSelectionAsJson,
+  formatSelectionAsSqlInList,
+  formatSelectionAsTsv,
+  isCellInSelection,
+  normalizeSelectionRange,
+} from "../src/lib/gridSelection.ts";
+
+test("normalizes a dragged cell range in either direction", () => {
+  const range = normalizeSelectionRange(
+    { rowIndex: 4, colIndex: 3 },
+    { rowIndex: 1, colIndex: 0 },
+  );
+
+  assert.deepEqual(range, {
+    startRow: 1,
+    endRow: 4,
+    startCol: 0,
+    endCol: 3,
+  });
+  assert.equal(isCellInSelection(2, 1, range), true);
+  assert.equal(isCellInSelection(5, 1, range), false);
+});
+
+test("extracts selection rows and columns from a rectangular range", () => {
+  const selection = extractSelection(
+    ["id", "name", "active"],
+    [
+      [1, "Ada", true],
+      [2, "Linus", false],
+      [3, null, true],
+    ],
+    { startRow: 0, endRow: 1, startCol: 1, endCol: 2 },
+  );
+
+  assert.deepEqual(selection.columns, ["name", "active"]);
+  assert.deepEqual(selection.rows, [
+    ["Ada", true],
+    ["Linus", false],
+  ]);
+});
+
+test("formats selected cells as TSV, CSV, JSON, and SQL values", () => {
+  const selection = {
+    columns: ["name", "note"],
+    rows: [
+      ["Ada", "math"],
+      ["Bob", "quote \"here\""],
+      ["O'Hara", null],
+    ],
+  };
+
+  assert.equal(formatSelectionAsTsv(selection), "name\tnote\nAda\tmath\nBob\tquote \"here\"\nO'Hara\tNULL");
+  assert.equal(formatSelectionAsCsv(selection), "\"name\",\"note\"\n\"Ada\",\"math\"\n\"Bob\",\"quote \"\"here\"\"\"\n\"O'Hara\",\"NULL\"");
+  assert.equal(
+    formatSelectionAsJson(selection),
+    JSON.stringify([
+      { name: "Ada", note: "math" },
+      { name: "Bob", note: "quote \"here\"" },
+      { name: "O'Hara", note: null },
+    ], null, 2),
+  );
+  assert.equal(formatSelectionAsSqlInList(selection), "('Ada', 'math', 'Bob', 'quote \"here\"', 'O''Hara', NULL)");
+});