create trigger\(em create a new trigger

.nf

\fBcreatetrigger\fR trigname\fB{before|after}\fP\fB{insert|update|delete}\fB

\fBcreatetrigger\fR trigname\fB{before|after}\fP

\fBon\fR relname\fBforeach{row|statement}\fR

\fBexecuteprocedure\fR funcname\fB(\fR arguments\fB)\fR

where\fBEventX\fR is one of INSERT, DELETE, UPDATE

.fi

.BR"Create Trigger"

and will execute the specified

.IR funcname.

Only relation owner may create a trigger on this relation.

Currently, STATEMENT triggers are not implemented.

.PP

The trigger can be specified to fire either

.BR before

.BR before

then the trigger may

skip the operation for the current tuple,

or changethe current tuple (for insert/delete operations only).

or changetuple being inserted (for insert/update operations only).

If the trigger fires

.BR after

then all changes including the last insertion/updation/deletion

drop trigger\(em destroy existingclasses

drop trigger\(em destroy existingtrigger

.nf

\fBdroptrigger\fR trigname

\fBdroptrigger\fR trigname\fBon\fR relname

.fi

.BR"Drop Trigger"

removestriggersfrom the data base.Onlyits owner may destroy a

removestrigger for relationfrom the data base. Onlyrelation owner may destroy a

trigger.

.nf

--

--Destroy the empverify trigger

--Destroy the empverify trigger on relation emp

--

drop trigger empverify

drop trigger empverify on emp

.fi

create trigger(l).