# Case statements
<a name="iot-sql-case"></a>

Case statements can be used for branching execution, like a switch statement.

Syntax:

```
CASE v WHEN t[1] THEN r[1] 
  WHEN t[2] THEN r[2] ... 
  WHEN t[n] THEN r[n] 
  ELSE r[e] END
```

The expression *`v`* is evaluated and matched for equality against the *`t[i]`* value of each `WHEN` clause. If a match is found, the corresponding *`r[i]`* expression becomes the result of the `CASE` statement. The `WHEN` clauses are evaluated in order so that if there's more than one matching clause, the result of the first matching clause becomes the result of the `CASE` statement. If there are no matches, *`r[e]`* of the `ELSE` clause is the result. If there's no match and no `ELSE` clause, the result is `Undefined`.

`CASE` statements require at least one `WHEN` clause. An `ELSE` clause is optional.

For example:

Incoming payload published on topic `topic/subtopic`:

```
{
    "color":"yellow"
}
```

SQL statement: 

```
SELECT CASE color
        WHEN 'green' THEN 'go'
        WHEN 'yellow' THEN 'caution'
        WHEN 'red' THEN 'stop'
        ELSE 'you are not at a stop light' END as instructions
    FROM 'topic/subtopic'
```

The resulting output payload would be:

```
{
    "instructions":"caution"
}
```

**Note**  
If *`v`* is `Undefined`, the result of the case statement is `Undefined`.