Updating of new row is not allowed in after trigger
Constraints are easier to write and less error-prone than triggers that enforce the same rules.
However, triggers can enforce some complex business rules that constraints cannot.
The name cannot be schema-qualified — the trigger inherits the schema of its table.This can only be specified for constraint triggers.An optional comma-separated list of arguments to be provided to the function when the trigger is executed. Simple names and numeric constants can be written here, too, but they will all be converted to strings.This can result in significant speedups in statements that modify many rows, if the trigger only needs to be fired for a few of the rows.
In triggers modify rows or prevent updates during an update that is caused by a referential action.Like a stored procedure, a trigger is a named PL/SQL unit that is stored in the database and can be invoked repeatedly.