# String slicing

[Read this page in HTML](https://www.scopedb.io/docs/reference/functions/string/substr)

Returns a range of Unicode characters from a string.

## Syntax

```scopeql
<string>[<start>:<end>]
<string>[:<end>]
<string>[<start>:]
<string>[:]
```

## Arguments

| Argument   | Type     | Description                                                                                                                    |
| ---------- | -------- | ------------------------------------------------------------------------------------------------------------------------------ |
| `<string>` | `string` | String to slice.                                                                                                               |
| `<start>`  | `int`    | Optional inclusive position, starting at 0. Negative values count from the end. Omitted or NULL starts at the first character. |
| `<end>`    | `int`    | Optional exclusive position. Negative values count from the end. Omitted or NULL continues to the end.                         |

## Returns

Returns `string`.

* Positions outside the string are limited to its start or end.
* If the adjusted start index is greater than or equal to the adjusted end index, returns an empty string.
* A NULL input returns NULL.

## Usage notes

Positions count Unicode characters, not UTF-8 bytes.

## Examples

### Read a fixed-format event identifier

Extract the producer prefix and sequence from an identifier with a known layout.

```scopeql
VALUES ('web-000017'), ('app-000042')
SELECT $0 AS event_id
SELECT event_id, event_id[:3] AS producer, event_id[-6:] AS sequence
```

```text
+------------+----------+----------+
| event_id   | producer | sequence |
+------------+----------+----------+
| web-000017 | web      | 000017   |
| app-000042 | app      | 000042   |
+------------+----------+----------+
```

The prefix excludes index 3; the negative start selects the last six characters.

### Preview international feedback

Take the first four characters of a customer message without splitting UTF-8 bytes.

```scopeql
SELECT '结账等待时间太长'[0:4] AS preview
```

```text
+----------+
| preview  |
+----------+
| 结账等待 |
+----------+
```