[Ratnesh]

Junction object is to achieve Many-to-Many relationship model in Salesforce. It means that each record can be associated with many records using the Junction object which keeps the reference of records.

Here is a example of junction object which shows many-to-many relationship in schema builder. Here junction object is user which show Many-to-Many relationship.

I hope picture will help you better to understand junction object.

[Ratnesh]

As Salesforce doesn’t save data in traditional way. Data of all tenants are in common table, so traditional Query
Use the Query Plan tool to optimise and speed up queries done over large numbers of records. View query plans for SOQL queries, SOSL searches, reports, and list views. If custom indexes are available for your organization, use query plans to help you decide when to request a custom index from Salesforce Support.

For more details visit here-https://help.salesforce.com/articleView?id=code_dev_console_tab_query_editor_query_plans.htm&type=5

[Ratnesh]

Various Cause may include are:-

Changing to auto-number except for text. Changing from text-area to e-mail, phone, URL, and text.

Changing from the multi-select picklist, checkbox, auto number to other types.

Migrating to percent, number, and currency from other data types.

Altering to multi-select picklist from any type except picklist.

Changing data and date-time.

[Ratnesh]

Recursion occurs when same code is executed again and again. It can lead to infinite loop and which can result to governor limit sometime. To avoid the situation of recursive call, we have to write code in such a way that the trigger will execute one time. To do so, we can create a class with a static Boolean variable with default value true

[Ratnesh]

Salesforce is the most used CRM as of now for most of the automation purposes.

Some of the email marketing company providers integration with salesforce to execute e-mails are

1. Mailchimp( comprised of a user-friendly interface and one among the best API.)
2. iContact (2x winner Best Mass Email App with full Salesforce integration, iContact for Salesforce can create, send and track emails at the campaign level, allowing for a direct measure of success in engaging, converting and retaining leads & contacts.)
3. Marketo, Eloqua, Silverpop, etc.

Tracking and other facilities are available in these apps.