---
title: Regex
noindex: true
canonical: https://docs.paradedb.com/documentation/advanced/term/regex
---

Regex queries search for terms that follow a pattern. For example, the wildcard pattern `key.*` finds all terms that start with `key`.

```sql
SELECT description, rating, category
FROM mock_items
WHERE description @@@ pdb.regex('key.*');
```

ParadeDB supports all regex constructs of the Rust [regex](https://docs.rs/regex/latest/regex/) crate, with the following exceptions:

1. Lazy quantifiers such as `+?`
2. Word boundaries such as `\b`

Otherwise, the full syntax of the [regex](https://docs.rs/regex/latest/regex/) crate is supported, including all Unicode support and relevant flags.

A list of regex flags and grouping options can be [found here](https://docs.rs/regex/latest/regex/#grouping-and-flags), which includes:

- named and numbered capture groups
- case insensitivty flag (`i`)
- multi-line mode (`m`)

<Note>
  Regex queries operate at the token level. To execute regex over the original
  text, use the keyword tokenizer.
</Note>

## Performance Considerations

During a regex query, ParadeDB doesn't scan through every single word. Instead, it uses a highly optimized structure called a [finite state transducer (FST)](https://en.wikipedia.org/wiki/Finite-state_transducer) that makes it possible to jump straight to the matching terms.
Even if the index contains millions of words, the regex query only looks at the ones that have a chance of matching, skipping everything else.

This is why the certain regex constructs are not supported -- they are difficult to implement efficiently.
