> ## Documentation Index
> Fetch the complete documentation index at: https://docs.firebolt.io/llms.txt
> Use this file to discover all available pages before exploring further.

> Reference material for SOUNDEX function

# SOUNDEX

Returns the Soundex code for a string. Soundex is a phonetic algorithm that indexes names by sound, as pronounced in English. The algorithm produces a four-character code consisting of a letter followed by three digits.

<Note>
  Non-alphabetic characters are ignored when generating the Soundex code. If the input string contains no alphabetic characters, SOUNDEX returns an empty string.
</Note>

## Syntax

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SOUNDEX(<expression>)
```

## Parameters

| Parameter      | Description                                        | Supported input types |
| :------------- | :------------------------------------------------- | :-------------------- |
| `<expression>` | The string for which to generate the Soundex code. | `TEXT`                |

## Return Type

`TEXT`

## Example

The following example generates Soundex codes for different variations of a name:

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT
    SOUNDEX('Smith') as soundex_smith,
    SOUNDEX('Smyth') as soundex_smyth,
    SOUNDEX('SMITH') as soundex_upper
```

**Returns**: `S530`, `S530`, `S530`

The following example shows the behavior with strings containing no alphabetic characters:

```sql theme={"theme":{"light":"github-light","dark":"github-dark"}}
SELECT
    SOUNDEX('123') as soundex_numbers,
    SOUNDEX('!@#$') as soundex_symbols,
    SOUNDEX('') as soundex_empty
```

**Returns**: `, `, \`\`