mirror of
https://github.com/lancedb/lancedb.git
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Jack Ye
fe651ae003
The function catalogue is now real rather than a pointer. Scalar functions are listed by taxonomy -- math, string, unicode, regex, date/time, array, map, struct, crypto, type -- and the names come from what datafusion-functions 54 actually registers, not from what DataFusion documents on main. Aggregate and window pages gain the same treatment. Two things the audit corrected rather than copied. SHOW TABLES does not work. DataFusion implements it over information_schema, which this session does not enable, so it fails at plan time. It was documented as working here, on the SHOW page and in three Manage tables; all four are fixed, and the SQL overview now lists the absence alongside SHOW COLUMNS. Prepared statements are a Flight SQL protocol feature, not a PREPARE statement. A script carrying PREPARE ... AS SELECT will not run, while the same intent expressed through a client will. The new page says so rather than copying DataFusion's syntax. Every section of the Documentation tab that has a SQL counterpart now links to it -- 27 of 76 non-SQL pages, each pointing at the specific statement rather than at the reference index.
94 lines
3.2 KiB
Plaintext
94 lines
3.2 KiB
Plaintext
---
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title: "Functions"
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sidebarTitle: "Functions"
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description: "Where to find each kind of function, and the dialect version they come from."
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icon: function
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keywords: ["functions", "datafusion", "scalar", "aggregate", "window", "fts", "table function"]
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---
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<Badge color="red">Enterprise</Badge> [SQL runs on a deployment.](/sql)
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LanceDB executes SQL with [Apache DataFusion](https://datafusion.apache.org),
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currently **version 54**. The function set is DataFusion's default registration
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plus what Lance adds.
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| --- | --- |
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| [Scalar functions](/sql/scalar-functions) | per row — math, string, regex, date/time, array, struct, JSON |
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| [Aggregate functions](/sql/aggregation#functions) | per group — `count`, `sum`, statistical, approximate |
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| [Window functions](/sql/window#functions) | per window — ranking, offset, running aggregates |
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| [Table functions](#table-functions) | produce a relation rather than a value |
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<Note>
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Function availability is version-specific. DataFusion adds functions in most
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releases, so one documented on `main` may not exist in 54. When a name is not
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recognised, check it against the reference for that version before assuming a
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bug.
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</Note>
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## Table functions {#table-functions}
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A table function appears in `FROM` and produces a relation, which is what lets
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it return columns a scalar function has nowhere to put.
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### `fts(table, query)` {#fts}
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Full-text search is a table function rather than a predicate, because it
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produces relevance alongside the matching rows:
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```sql
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SELECT id, text, _score
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FROM fts('my_docs', 'puppy')
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ORDER BY _score DESC
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LIMIT 5
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```
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The second argument is a bare query string, or a JSON query object for the
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fuzzy, phrase, boolean, boost and multi-match forms.
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Its schema is the dataset's, so every column of the table is available in the
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result and projections push into the scan rather than being applied afterwards.
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Being a relation is also what makes it compose — join it, filter it, aggregate
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over it:
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```sql
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SELECT c.name, count(*) AS hits
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FROM fts('my_docs', 'puppy') AS m
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JOIN categories AS c ON c.id = m.category_id
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GROUP BY c.name
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ORDER BY hits DESC
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```
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For a keyword test that needs no score, the
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[`contains_tokens`](/sql/scalar-functions#contains-tokens) predicate is
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index-accelerated and usable directly in `WHERE`.
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### `_score` {#score}
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A pseudo-column produced by `fts()`, carrying relevance for the row. It behaves
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like any other column — order by it, filter on it, project it — and exists only
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in a relation that came from `fts()`. See
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[Data types](/sql/data-types#pseudo-columns).
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### `generate_series` {#generate-series}
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```sql
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SELECT * FROM generate_series(1, 10)
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```
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Rows from a range, useful for building a dense axis to left-join sparse data
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onto.
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## What Lance accelerates {#accelerated}
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Two function families use an index rather than scanning, which is the difference
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between a fast predicate and a slow one:
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| | Index used |
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| --- | --- |
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| [`contains_tokens`](/sql/scalar-functions#contains-tokens) | full-text index |
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| [`json_get`, typed variants, `json_extract`](/sql/scalar-functions#json) | JSON scalar index |
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Confirm with [`EXPLAIN`](/sql/explain): an accelerated predicate shows an index
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node rather than a `LanceScan` followed by a filter.
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