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A trigger is a statement or a block of statement which are executed automatically by the system when an event like insert, update or delete takes place on a table.

But I don't know where we use assertion and where we use trigger in database. Can anyone explain,

What is assertion and difference between the assertion and trigger?

  • By assertion, do you mean constraints, like CHECK constraints? – Craig Ringer Nov 8 '16 at 5:44
  • Yes, I mean like constraint. – nidipa nima Nov 8 '16 at 6:00
  • Yes, I asked the meaning like asserts – nidipa nima Nov 8 '16 at 6:01
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The difference between triggers and assertions are:

Triggers - a trigger is a piece of SQL to execute either before or after an update, insert, or delete in a database.

An example of a trigger in plain English might be something like: before updating a customer record, save a copy of the current record. Which would look something like:

CREATE TRIGGER triggerName
AFTER UPDATE
    INSERT INTO CustomerLog (blah, blah, blah)
    SELECT blah, blah, blah FROM deleted

Assertions - An assertion is a piece of SQL which makes sure a condition is satisfied or it stops action being taken on a database object. It could mean locking out the whole table or even the whole database.

Triggers - Triggers are more powerful because the can check conditions and also modify the data

Assertions - Assertions do not modify the data, they only check certain conditions.

Triggers - Triggers are linked to specific tables and specific events.

Assertions - Assertions are not linked to specific tables in the database and not linked to specific events.

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