feat(Merge Node): Better pairedItem mapping in combineBySql operation if SELECT query (#13849)

Co-authored-by: Shireen Missi <94372015+ShireenMissi@users.noreply.github.com>

packages/nodes-base/nodes/Merge/v3/helpers/utils.ts

@@ -386,3 +386,43 @@ export function getNodeInputsData(this: IExecuteFunctions) {
 
 	return returnData;
 }
+
+export const rowToExecutionData = (data: IDataObject): INodeExecutionData => {
+	const keys = Object.keys(data);
+	const pairedItem: IPairedItemData[] = [];
+	const json: IDataObject = {};
+
+	for (const key of keys) {
+		if (key.startsWith('pairedItem')) {
+			if (data[key] === undefined) continue;
+			pairedItem.push(data[key] as IPairedItemData);
+		} else {
+			json[key] = data[key];
+		}
+	}
+
+	return { json, pairedItem };
+};
+
+export function modifySelectQuery(userQuery: string, inputLength: number): string {
+	const selectMatch = userQuery.match(/SELECT\s+(.+?)\s+FROM/i);
+	if (!selectMatch) return userQuery;
+
+	let selectedColumns = selectMatch[1].trim();
+
+	if (selectedColumns === '*') {
+		return userQuery;
+	}
+
+	const pairedItemColumns = [];
+
+	for (let i = 1; i <= inputLength; i++) {
+		if (userQuery.includes(`input${i}`)) {
+			pairedItemColumns.push(`input${i}.pairedItem AS pairedItem${i}`);
+		}
+	}
+
+	selectedColumns += pairedItemColumns.length ? ', ' + pairedItemColumns.join(', ') : '';
+
+	return userQuery.replace(selectMatch[0], `SELECT ${selectedColumns} FROM`);
+}