# lec10

This lecture has a corresponding lab excercise who's instructions can be found in `triggers-lab.pdf`.

## What is a trigger

Something that executes when _some operation_ is performed

## Structure 

```
create trigger NAME before some_operation
when(condition)
begin
	do_something
end;
```

To explain: First we `create trigger` followed by some trigger name.
Then we have to denote that this trigger should fire whenever some operation happens.
This trigger then executes everything in the `begin...end;` section _before_ the new operation happens.

> `after`

Likewise if we want to fire a trigger _after_ some operation we ccan just replace the before keyword with `after`.

> `new.adsf`

Refers to _new_ value being added to a table.

> `old.adsf` 

Refers to _old_ vvalue being changed in a table.

	
## Trigger Metadata

If you want to look at what triggers exist you can query the `sql_master` table.

```
select * from sql_master where name='trigger';
```