# Procedural Constructs

## Compound Statements

Refers to a set of SQL statements written between **begin** and **end**.

## Loops

### while

```
declare n integer default 0; 
while n < 10 do 
  set n = n + 1 
end while
```

### repeat

```
repeat 
 set n = n – 1 
until n = 0 
end repeat
```

### for

Permits iteration over all results of a query.

For example:

```
declare n integer default 0;
for r as
  select budget from department
  where dept_name = 'Music'
do
  set n = n - r.budget
end for
```

* **leave** is used to exit the loop
* **iterate** starts from the next tuple

## Conditional Constructs

SQL also supports conditional constructs such as **if-then-else** and **case**.

## Exception Handling

Example:

```
declare out_of_classroom_seats condition
declare exit handler for out_of_classroom_seats
begin
...
.. signal out_of_classroom_seats
end
```

**exit** is the handler; it causes the block enclosed by begin..end to be exited.