What are Apex Triggers?
Typically, you use triggers to perform operations based on specific conditions, to modify related records, or restrict certain operations from happening. You can use triggers to do anything you can do in Apex, including executing SOQL and DML or calling custom Apex methods.
Use triggers to perform tasks that can’t be done by using the point-and-click tools in the Salesforce user interface. For example, if validating a field value or updating a field on a record, use validation rules and workflow rules instead.
Triggers can be defined for top-level standard objects, such as Account or Contact, custom objects, and some standard child objects. Triggers are active by default when created. Salesforce automatically fires active triggers when the specified database events occur.
Here you can check out the 36 Awesome trigger scenarios for practice in Salesforce
Link: Apex Triggers
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