Answer / kumar jabu

Constraints implements specific conduct or rules on table column like it determines whether field data should be unique,not null ..
But triiger implements rules on systems or application event.
whenever dml occurs that implemented rules been fired.

Answer / naga sindhuri

Triggers not apply for existing rows but constraints can
apply for existing rows.

Answer / milind chopde

1) Constraints can be used for validation but trigger can be used for complex validation and auditing purpose.
2) Trigger is database object but constraint not.
3) Trigger can be fired on DDL commands but constraints are created or altered using DDL commands.
4) Trigger can be fired on particular event like before/after DML but constraint always check before any data insert or update to table.

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