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/actions/mode/combineBySql.ts

@@ -1,8 +1,11 @@
+import { Container } from '@n8n/di';
 import alasql from 'alasql';
 import type { Database } from 'alasql';
+import { ErrorReporter } from 'n8n-core';
 import type {
 	IDataObject,
 	IExecuteFunctions,
+	INode,
 	INodeExecutionData,
 	INodeProperties,
 	IPairedItemData,
@@ -12,6 +15,7 @@ import { NodeOperationError } from 'n8n-workflow';
 import { getResolvables, updateDisplayOptions } from '@utils/utilities';
 
 import { numberInputsProperty } from '../../helpers/descriptions';
+import { modifySelectQuery, rowToExecutionData } from '../../helpers/utils';
 
 export const properties: INodeProperties[] = [
 	numberInputsProperty,
@@ -39,15 +43,102 @@ const displayOptions = {
 
 export const description = updateDisplayOptions(displayOptions, properties);
 
+const prepareError = (node: INode, error: Error) => {
+	let message = '';
+	if (typeof error === 'string') {
+		message = error;
+	} else {
+		message = error.message;
+	}
+	throw new NodeOperationError(node, error, {
+		message: 'Issue while executing query',
+		description: message,
+		itemIndex: 0,
+	});
+};
+
+async function executeSelectWithMappedPairedItems(
+	node: INode,
+	inputsData: INodeExecutionData[][],
+	query: string,
+): Promise<INodeExecutionData[][]> {
+	const returnData: INodeExecutionData[] = [];
+
+	const db: typeof Database = new (alasql as any).Database(node.id);
+
+	try {
+		for (let i = 0; i < inputsData.length; i++) {
+			const inputData = inputsData[i];
+
+			db.exec(`CREATE TABLE input${i + 1}`);
+			db.tables[`input${i + 1}`].data = inputData.map((entry) => ({
+				...entry.json,
+				pairedItem: entry.pairedItem,
+			}));
+		}
+	} catch (error) {
+		throw new NodeOperationError(node, error, {
+			message: 'Issue while creating table from',
+			description: error.message,
+			itemIndex: 0,
+		});
+	}
+
+	try {
+		const result: IDataObject[] = db.exec(modifySelectQuery(query, inputsData.length));
+
+		for (const item of result) {
+			if (Array.isArray(item)) {
+				returnData.push(...item.map((entry) => rowToExecutionData(entry)));
+			} else if (typeof item === 'object') {
+				returnData.push(rowToExecutionData(item));
+			}
+		}
+
+		if (!returnData.length) {
+			returnData.push({ json: { success: true } });
+		}
+	} catch (error) {
+		prepareError(node, error as Error);
+	} finally {
+		delete alasql.databases[node.id];
+	}
+
+	return [returnData];
+}
+
 export async function execute(
 	this: IExecuteFunctions,
 	inputsData: INodeExecutionData[][],
 ): Promise<INodeExecutionData[][]> {
-	const nodeId = this.getNode().id;
+	const node = this.getNode();
 	const returnData: INodeExecutionData[] = [];
 	const pairedItem: IPairedItemData[] = [];
 
-	const db: typeof Database = new (alasql as any).Database(nodeId);
+	let query = this.getNodeParameter('query', 0) as string;
+
+	for (const resolvable of getResolvables(query)) {
+		query = query.replace(resolvable, this.evaluateExpression(resolvable, 0) as string);
+	}
+
+	const isSelectQuery = node.typeVersion >= 3.1 ? query.toLowerCase().startsWith('select') : false;
+
+	if (isSelectQuery) {
+		try {
+			return await executeSelectWithMappedPairedItems(node, inputsData, query);
+		} catch (error) {
+			Container.get(ErrorReporter).error(error, {
+				extra: {
+					nodeName: node.name,
+					nodeType: node.type,
+					nodeVersion: node.typeVersion,
+					workflowId: this.getWorkflow().id,
+				},
+			});
+		}
+	}
+
+	const db: typeof Database = new (alasql as any).Database(node.id);
 
 	try {
 		for (let i = 0; i < inputsData.length; i++) {
@@ -90,7 +181,7 @@ export async function execute(
 			db.tables[`input${i + 1}`].data = inputData.map((entry) => entry.json);
 		}
 	} catch (error) {
-		throw new NodeOperationError(this.getNode(), error, {
+		throw new NodeOperationError(node, error, {
 			message: 'Issue while creating table from',
 			description: error.message,
 			itemIndex: 0,
@@ -98,12 +189,6 @@ export async function execute(
 	}
 
 	try {
-		let query = this.getNodeParameter('query', 0) as string;
-
-		for (const resolvable of getResolvables(query)) {
-			query = query.replace(resolvable, this.evaluateExpression(resolvable, 0) as string);
-		}
-
 		const result: IDataObject[] = db.exec(query);
 
 		for (const item of result) {
@@ -118,20 +203,10 @@ export async function execute(
 			returnData.push({ json: { success: true }, pairedItem });
 		}
 	} catch (error) {
-		let message = '';
-		if (typeof error === 'string') {
-			message = error;
-		} else {
-			message = error.message;
-		}
-		throw new NodeOperationError(this.getNode(), error, {
-			message: 'Issue while executing query',
-			description: message,
-			itemIndex: 0,
-		});
+		prepareError(node, error as Error);
+	} finally {
+		delete alasql.databases[node.id];
 	}
 
-	delete alasql.databases[nodeId];
-
 	return [returnData];
 }