---
layout: docu
railroad: expressions/function.js
title: Functions
---

## Function Syntax

<div id="rrdiagram"></div>

## Function Chaining via the Dot Operator

DuckDB supports the dot syntax for function chaining. This allows the function call `fn(arg1, arg2, arg3, ...)` to be rewritten as `arg1.fn(arg2, arg3, ...)`. For example, take the following use of the [`replace` function]({% link docs/1.3/sql/functions/text.md %}#replacestring-source-target):

```sql
SELECT replace(goose_name, 'goose', 'duck') AS duck_name
FROM unnest(['African goose', 'Faroese goose', 'Hungarian goose', 'Pomeranian goose']) breed(goose_name);
```

This can be rewritten as follows:

```sql
SELECT goose_name.replace('goose', 'duck') AS duck_name
FROM unnest(['African goose', 'Faroese goose', 'Hungarian goose', 'Pomeranian goose']) breed(goose_name);
```

### Using with Literals and Arrays

To apply function chaining to literals and following array access operations, you must surround the argument with parentheses, e.g.:

```sql
SELECT ('hello world').replace(' ', '_');
```

```sql
SELECT (2).sqrt();
```

```sql
SELECT (m[1]).map_entries()
FROM (VALUES ([MAP {'hello': 42}, MAP {'world': 42}])) t(m);
```

In the absence of these parentheses, DuckDB will return a `Parser Error` for the function call:

```console
Parser Error:
syntax error at or near "("
```

### Limitations

Function chaining via the dot operator is limited to *scalar* functions and is not supported for *table* functions.
For example, the following call returns a `Parser Error`:

```sql
SELECT * FROM ('my_file.parquet').read_parquet(); -- does not work
```

## Query Functions

The `duckdb_functions()` table function shows the list of functions currently built into the system.

```sql
SELECT DISTINCT ON(function_name)
    function_name,
    function_type,
    return_type,
    parameters,
    parameter_types,
    description
FROM duckdb_functions()
WHERE function_type = 'scalar'
  AND function_name LIKE 'b%'
ORDER BY function_name;
```

| function_name | function_type | return_type |       parameters       |         parameter_types          |                                                               description                                                                |
|---------------|---------------|-------------|------------------------|----------------------------------|------------------------------------------------------------------------------------------------------------------------------------------|
| bar           | scalar        | VARCHAR     | [x, min, max, width]   | [DOUBLE, DOUBLE, DOUBLE, DOUBLE] | Draws a band whose width is proportional to (x - min) and equal to width characters when x = max. width defaults to 80                   |
| base64        | scalar        | VARCHAR     | [blob]                 | [BLOB]                           | Convert a blob to a base64 encoded string                                                                                                |
| bin           | scalar        | VARCHAR     | [value]                | [VARCHAR]                        | Converts the value to binary representation                                                                                              |
| bit_count     | scalar        | TINYINT     | [x]                    | [TINYINT]                        | Returns the number of bits that are set                                                                                                  |
| bit_length    | scalar        | BIGINT      | [col0]                 | [VARCHAR]                        | NULL                                                                                                                                     |
| bit_position  | scalar        | INTEGER     | [substring, bitstring] | [BIT, BIT]                       | Returns first starting index of the specified substring within bits, or zero if it is not present. The first (leftmost) bit is indexed 1 |
| bitstring     | scalar        | BIT         | [bitstring, length]    | [VARCHAR, INTEGER]               | Pads the bitstring until the specified length                                                                                            |

> Currently, the description and parameter names of functions are not available in the `duckdb_functions()` function.