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> Reference material for CASE function

# CASE

Conditional expression similar to if-then-else statements.
If the result of the condition is true, then the value of the CASE expression is the result that follows the condition, and the remainder of the CASE expression is not processed. If the result is not true, any subsequent WHEN clauses (conditions) are evaluated in the same manner. If no WHEN condition is true, then the value of the case expression is the result specified in the ELSE clause.  If the ELSE clause is omitted and no condition matches, the result is NULL.

## Syntax

```sql theme={"theme":{"light":"css-variables","dark":"css-variables"}}
CASE
    WHEN <condition> THEN <result>
    [ WHEN ...n ]
    [ ELSE <result> ]
END;
```

## Parameters

| Parameter     | Description                                                                                                                                                                                  | Supported input types |
| :------------ | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | :-------------------- |
| `<condition>` | A condition can be defined for each `WHEN` clause.                                                                                                                                           | `BOOLEAN`             |
| `<result>`    | The result of the CASE expression when the preceding condition holds. Every `THEN` clause receives a single result. All results in a single `CASE` expression must share the same data type. | Any                   |

## Return type

Same data type as `<result>`

## Example

The following example categorizes each level in the `levels` table into a difficulty tier based on its level number:

<div className="query-window">
  ```
  SELECT level, name,
    CASE
      WHEN level <= 3 THEN 'Beginner'
      WHEN level <= 7 THEN 'Intermediate'
      ELSE 'Expert'
    END AS difficulty
  FROM levels
  ORDER BY level;
  ```

  | level <span>int null</span> | name <span>text null</span> | difficulty <span>text</span> |
  | :-------------------------- | :-------------------------- | :--------------------------- |
  | 1                           | Thunderbolt Circuit         | Beginner                     |
  | 2                           | Velocity Vale               | Beginner                     |
  | 3                           | Raceway Ridge               | Beginner                     |
  | 4                           | Nitro Narrows               | Intermediate                 |
  | 5                           | Thunder Road                | Intermediate                 |
  | 6                           | Burnout Boulevard           | Intermediate                 |
  | 7                           | Speed Street                | Intermediate                 |
  | 8                           | Racing Ravine               | Expert                       |
  | 9                           | Drift District              | Expert                       |
  | 10                          | Acceleration Alley          | Expert                       |

  <p><span>Rows: 10</span><span>Execution time: 6.00ms</span></p>
</div>