Different between trigger and workflow

Workflow

Workflow is an automated process that fired an action based on Evaluation criteria and rule criteria.

We can access a workflow across the object.

We cannot perform DML operation on workflow

 We cannot query from database

Trigger

Trigger is a piece of code that executes before or after a record is inserted or updated.

We can access the trigger across the object and related to that objects

We can use 20 DML operations in one trigger.

We can use 20 SOQL’s from database in one trigger.

Workflows are retired.

Please find the diifference between trigger and workflow.

Triggers:
1. Trigger can work across objects.
2. Trigger works before and after some actions + On different DML actions like Insert, Update, Delete, Undelete
3. Coding is required.
4. Often needed for roll-up type scenarios where roll up summary fields cannot be used and also when a record needs to be created on a different object

Workflow rules:
1. Workflow Rules will be helpful to update the same object or master object in custom master-detail relationships.
2. Coding is not required and they currently can only result in a task, email, field update, or outbound message
3. Workflows work only after some actions i.e. entry criteria's
4. they can only cross objects in a master detail relationship, from the detail to the master, and only for certain scenarios (all custom to custom objects, some custom to standard objects, and even fewer standard to standard) https://help.salesforce.com/HTViewHelpDoc?id=workflow_cross_object_field_updates.htm&language=en_US
5. you cannot create records from WF

Here are the some differencies between trigger and workflow

Workflow:

• Workflow is automated process that fired an action based on Evaluation criteria and rule criteria.
• Workflow Rules will be helpful to update the same object or master object in custom master-detail relationships.
• We cannot query from database
• Coding is not required.
• Workflows work only after some actions.
• We can access a workflow across the object.
• We cannot perform DML operation on workflow

Trigger:

• Trigger is a piece of code that executes before or after a record is inserted or updated.
• We can access the trigger across the object and related to that objects
• Coding is required.
• Trigger works before and after some actions.
• Trigger can work across objects.
• We can use 20 DML operations in one trigger.