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

# User-Defined Functions

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A user-defined function (UDF) is a named function defined at the database level that can be called in queries and other contexts. CockroachDB supports invoking UDFs in `SELECT`, `FROM`, and `WHERE` clauses of <InternalLink path="sql-statements#data-manipulation-statements">DML statements</InternalLink>.

Both <InternalLink path="stored-procedures">stored procedures</InternalLink> and user-defined functions are types of *routines*. However, they differ in the following ways:

* Functions return a value, and procedures do not return a value.
* Procedures must be invoked using a <InternalLink path="call">`CALL`</InternalLink> statement. Functions can be invoked in nearly any context, such as `SELECT`, `FROM`, and `WHERE` clauses, <InternalLink path="default-value">`DEFAULT`</InternalLink> expressions, and <InternalLink path="computed-columns">computed column</InternalLink> expressions.
* Functions have <InternalLink path="functions-and-operators#function-volatility">volatility</InternalLink> settings, and procedures do not.

## Overview

The basic components of a user-defined function are a name, list of arguments, return type, volatility, language, and function body.

* An argument has a *mode* and a *type*.
  * CockroachDB supports the `IN` (default), `OUT`, and `INOUT` argument modes. For an example, see <InternalLink path="create-function#create-a-function-that-uses-out-and-inout-parameters">Create a function that uses `OUT` and `INOUT` parameters</InternalLink>.
  * The type can be a built-in type, <InternalLink path="enum">user-defined `ENUM`</InternalLink> or <InternalLink path="create-type#create-a-composite-data-type">composite</InternalLink> type, or implicit record type. A type can have a `DEFAULT` value.
* The return type can be a built-in <InternalLink path="data-types">SQL type</InternalLink>, user-defined <InternalLink path="enum">`ENUM`</InternalLink> or <InternalLink path="create-type#create-a-composite-data-type">composite</InternalLink> type, <InternalLink path="create-function#create-a-function-that-returns-a-record-type">`RECORD`</InternalLink>, PL/pgSQL <InternalLink path="plpgsql#declare-cursor-variables">`REFCURSOR`</InternalLink> type, implicit record type, <InternalLink path="triggers#trigger-function">`TRIGGER`</InternalLink>, or `VOID`.
  * Preceding a type with `SETOF` indicates that a set, or multiple rows, may be returned. For an example, see <InternalLink path="create-function#create-a-function-that-returns-a-set-of-results">Create a function that returns a set of results</InternalLink>.
  * `VOID` indicates that there is no return type and `NULL` will always be returned.
* The <InternalLink path="functions-and-operators#function-volatility">volatility</InternalLink> indicates whether the function has side effects. `VOLATILE` and `NOT LEAKPROOF` are the default.
  * Annotate a function with side effects with `VOLATILE`. This also prevents the <InternalLink path="cost-based-optimizer">cost-based optimizer</InternalLink> from pre-evaluating the function.
  * A `STABLE` or `IMMUTABLE` function does not mutate data. You cannot create a `STABLE` or `IMMUTABLE` function that executes a mutation ( `INSERT`, `UPSERT`, `UPDATE`, `DELETE` ) statement.
  * `LEAKPROOF` indicates that a function has no side effects and that it communicates nothing that depends on its arguments besides the return value (i.e., it cannot throw an error that depends on the value of its arguments). You must precede `LEAKPROOF` with `IMMUTABLE`, and only `IMMUTABLE` can be set to `LEAKPROOF`. `NOT LEAKPROOF` is allowed with any other volatility.
  * Non- `VOLATILE` functions can be optimized through inlining. For more information, see [Create an inlined UDF](#create-an-inlined-udf).
* `LANGUAGE` specifies the language of the function body. CockroachDB supports the languages `SQL` and <InternalLink path="plpgsql">`PLpgSQL` (PL/pgSQL)</InternalLink>.
* The function body:
  * Can reference arguments by name or by their ordinal in the function definition with the syntax `$1`.
  * Can be enclosed in a single line with single quotes `''` or multiple lines with `$$`.
  * Can reference tables.
  * Can reference only the `SELECT` statement.

## Examples

### Create a UDF

The following is a UDF that returns the sum of two integers:

```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
CREATE FUNCTION add(a INT, b INT) RETURNS INT IMMUTABLE LEAKPROOF LANGUAGE SQL AS 'SELECT a + b';
```

Where:

* name: `add`
* arguments: `a` of type `INT`, `b` of type `INT`
* return type: `INT`
* volatility: `IMMUTABLE LEAKPROOF`
* language: `SQL`
* function body: `'SELECT a + b'`

Alternatively, you could define this function as:

```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
CREATE FUNCTION add(a INT, b INT) RETURNS INT IMMUTABLE LEAKPROOF LANGUAGE SQL AS 'SELECT $1 + $2';
```

Or as:

```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
CREATE FUNCTION add(a INT, b INT) RETURNS INT LANGUAGE SQL AS $$
  SELECT a + b;
$$;
```

For more examples of UDF creation, see <InternalLink path="create-function">`CREATE FUNCTION`</InternalLink>.

### View a UDF definition

To view the definition for the `add()` function:

```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
SHOW CREATE FUNCTION add;
```

If you do not specify a schema for the function `add` when you create it, the default schema is `public`:

```text theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
  function_name |                 create_statement
----------------+---------------------------------------------------
 add            | CREATE FUNCTION public.add(IN a INT8, IN b INT8)
                |     RETURNS INT8
                |     IMMUTABLE
                |     LEAKPROOF
                |     CALLED ON NULL INPUT
                |     LANGUAGE SQL
                |     AS $$
                |     SELECT a + b;
                | $$
(1 row)
```

### Invoke a UDF

You invoke a UDF like a <InternalLink path="functions-and-operators">built-in function</InternalLink>.

To invoke the `add()` function:

```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
SELECT add(3,5) as sum;
```

```text theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
  sum
-------
    8
(1 row)
```

### Create a UDF using PL/pgSQL

The following user-defined function returns the `n`th integer in the Fibonacci sequence.

It uses the <InternalLink path="plpgsql">PL/pgSQL</InternalLink> <InternalLink path="plpgsql#write-loops">`LOOP`</InternalLink> syntax to iterate through a simple calculation, and <InternalLink path="plpgsql#report-messages-and-handle-exceptions">`RAISE EXCEPTION`</InternalLink> to return an error message if the specified `n` is negative.

```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
CREATE FUNCTION fib(n int) RETURNS INT AS $$
    DECLARE
        tmp INT;
        a INT := 0;
        b INT := 1;
        i INT := 2;
    BEGIN
        IF n < 0 THEN
            RAISE EXCEPTION 'n must be non-negative';
        END IF;
        IF n = 0 THEN RETURN 0; END IF;
        IF n = 1 THEN RETURN 1; END IF;
        LOOP
            IF i > n THEN EXIT; END IF;
            tmp := a + b;
            a := b;
            b := tmp;
            i := i + 1;
        END LOOP;
        RETURN b;
    END
  $$ LANGUAGE PLpgSQL;
```

```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
SELECT fib(8);
```

```text theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
  fib
-------
   21
```

### Create an inlined UDF

When possible, the <InternalLink path="cost-based-optimizer">cost-based optimizer</InternalLink> will improve a function's performance by inlining the UDF within the query plan. The UDF must have the following attributes:

* It is labeled as `IMMUTABLE`, `STABLE`, or `LEAKPROOF` (i.e., non- `VOLATILE` ).
* It has a single statement.
* It is not a <InternalLink path="create-function#create-a-function-that-returns-a-set-of-results">set-returning function</InternalLink>.
* Its arguments are only variable or constant expressions.
* It is not a <InternalLink path="create-function#create-a-function-that-returns-a-record-type">record-returning function</InternalLink>.

The following example demonstrates how inlining improves a UDF's performance.

1. Create tables `a` and `b`:

   ```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   CREATE TABLE a (
     a INT
   );

   CREATE TABLE b (
     b INT PRIMARY KEY
   );
   ```
2. Insert a value (`10`) into 1000 rows in `a` and 1 row in `b`:

   ```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   INSERT INTO a SELECT 10 FROM generate_series(1, 1000);
   INSERT INTO b VALUES (10);
   ```
3. Create a `VOLATILE` function `foo_v()` and a `STABLE` function `foo_s()`:

   ```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   CREATE FUNCTION foo_v(x INT) RETURNS INT VOLATILE LANGUAGE SQL AS $$
     SELECT b FROM b WHERE b = x
   $$;

   CREATE FUNCTION foo_s(x INT) RETURNS INT STABLE LANGUAGE SQL AS $$
     SELECT b FROM b WHERE b = x
   $$;
   ```

   Each function returns a specified value from table `b`.
4. View the query plan when `foo_v()` (the `VOLATILE` function) is used in a selection query to retrieve equal values from table `a`:

   ```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   EXPLAIN ANALYZE SELECT foo_v(a) FROM a WHERE a = 10;
   ```

   ```text theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
                                               info
   --------------------------------------------------------------------------------------------
     planning time: 2ms
     execution time: 77ms
     distribution: local
     vectorized: true
     rows read from KV: 1,000 (39 KiB, 1 gRPC calls)
     cumulative time spent in KV: 330µs
     maximum memory usage: 80 KiB
     network usage: 0 B (0 messages)
     sql cpu time: 75ms
     estimated RUs consumed: 0

     • render
     │
     └── • filter
         │ nodes: n1
         │ actual row count: 1,000
         │ sql cpu time: 75ms
         │ estimated row count: 1,000
         │ filter: a = 10
         │
         └── • scan
               nodes: n1
               actual row count: 1,000
               KV time: 330µs
               KV contention time: 0µs
               KV rows read: 1,000
               KV bytes read: 39 KiB
               KV gRPC calls: 1
               estimated max memory allocated: 60 KiB
               sql cpu time: 87µs
               estimated row count: 1,000 (100% of the table; stats collected 19 seconds ago)
               table: a@a_pkey
               spans: FULL SCAN
   (33 rows)
   ```

   The query takes `77ms` to execute because the function is invoked for each row scanned in table `a`.
5. View the query plan when using `foo_s()` (the `STABLE` function) instead:

   ```sql theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
   EXPLAIN ANALYZE SELECT foo_s(a) FROM a WHERE a = 10;
   ```

   ```text theme={"theme":{"light":"catppuccin-mocha","dark":"catppuccin-mocha"}}
                                                 info
   ------------------------------------------------------------------------------------------------
     planning time: 5ms
     execution time: 4ms
     distribution: local
     vectorized: true
     rows read from KV: 1,001 (39 KiB, 2 gRPC calls)
     cumulative time spent in KV: 832µs
     maximum memory usage: 420 KiB
     network usage: 0 B (0 messages)
     sql cpu time: 3ms
     estimated RUs consumed: 0

     • render
     │
     └── • merge join (left outer)
         │ nodes: n1
         │ actual row count: 1,000
         │ estimated max memory allocated: 340 KiB
         │ estimated max sql temp disk usage: 0 B
         │ sql cpu time: 3ms
         │ estimated row count: 1,000
         │ equality: (a) = (b)
         │ right cols are key
         │
         ├── • filter
         │   │ nodes: n1
         │   │ actual row count: 1,000
         │   │ sql cpu time: 5µs
         │   │ estimated row count: 1,000
         │   │ filter: a = 10
         │   │
         │   └── • scan
         │         nodes: n1
         │         actual row count: 1,000
         │         KV time: 722µs
         │         KV contention time: 0µs
         │         KV rows read: 1,000
         │         KV bytes read: 39 KiB
         │         KV gRPC calls: 1
         │         estimated max memory allocated: 60 KiB
         │         sql cpu time: 202µs
         │         estimated row count: 1,000 (100% of the table; stats collected 42 seconds ago)
         │         table: a@a_pkey
         │         spans: FULL SCAN
         │
         └── • scan
               nodes: n1
               actual row count: 1
               KV time: 110µs
               KV contention time: 0µs
               KV rows read: 1
               KV bytes read: 30 B
               KV gRPC calls: 1
               estimated max memory allocated: 20 KiB
               sql cpu time: 11µs
               estimated row count: 1 (100% of the table; stats collected 42 seconds ago)
               table: b@b_pkey
               spans: FULL SCAN
   (57 rows)
   ```

   The query takes only `4ms` to execute because the function is inlined and transformed to a <InternalLink path="joins">join</InternalLink> with an equality comparison `(a) = (b)`, which has much less overhead than invoking a function for each row scanned in table `a`.

### Video Demo

For a deep-dive demo on UDFs, watch the following video:

## Known limitations

User-defined functions have the following limitations:

* A `RECORD` -returning UDF cannot be created without a `RETURN` statement in the root block, which would restrict the wildcard type to a concrete one.
* User-defined functions are not currently supported in:
  * Expressions (column, index, constraint) in tables.
  * Views.
* User-defined functions cannot call themselves recursively.
* <InternalLink path="common-table-expressions">Common table expressions</InternalLink> (CTE), recursive or non-recursive, are not supported in <InternalLink path="user-defined-functions">user-defined functions</InternalLink> (UDF). That is, you cannot use a `WITH` clause in the body of a UDF.
* The `setval` function cannot be resolved when used inside UDF bodies.
* Casting subqueries to <InternalLink path="create-type">user-defined types</InternalLink> in UDFs is not supported.
* Routines cannot be invoked with named arguments, e.g., `SELECT foo(a => 1, b => 2);` or `SELECT foo(b:= 1, a:= 2);`.
* Routines cannot be created if they reference temporary tables.
* Routines cannot be created with unnamed `INOUT` parameters. For example, `CREATE PROCEDURE p(INOUT INT) AS $$ BEGIN NULL; END; $$ LANGUAGE PLpgSQL;`.
* Routines cannot be created if they return fewer columns than declared. For example, `CREATE FUNCTION f(OUT sum INT, INOUT a INT, INOUT b INT) LANGUAGE SQL AS $$ SELECT (a + b, b); $$;`.
* Routines cannot be created with an `OUT` parameter of type `RECORD`.
* DDL statements (e.g., `CREATE TABLE`, `CREATE INDEX`) are not allowed within UDFs or stored procedures.
* Polymorphic types cannot be cast to other types (e.g., `TEXT`) within routine parameters.
* Routine parameters and return types cannot be declared using the `ANYENUM` polymorphic type, which is able to match any <InternalLink path="enum">`ENUM`</InternalLink> type. 123048

Also refer to the <InternalLink path="plpgsql#known-limitations">PL/pgSQL known limitations</InternalLink>.

## See also

* <InternalLink path="create-function">`CREATE FUNCTION`</InternalLink>
* <InternalLink path="alter-function">`ALTER FUNCTION`</InternalLink>
* <InternalLink path="drop-function">`DROP FUNCTION`</InternalLink>
* <InternalLink path="show-create">`SHOW CREATE`</InternalLink>
* <InternalLink path="sql-statements">SQL Statements</InternalLink>
* <InternalLink path="functions-and-operators">Functions and Operators</InternalLink>