---
metadata:
  - name: generator
    content: Diplodoc Platform v5.50.6
alternate:
  - https://ydb.tech/docs/en/yql/reference/syntax/action.md?version=main
  - https://ydb.tech/docs/ru/yql/reference/syntax/action.md?version=main
sourcePath: en/core/yql/reference/syntax/action.md
---
> **Documentation Index:** Fetch the complete configuration index at https://ydb.tech/docs/en/llms.txt

# ACTION

## DEFINE ACTION {#define-action}

Specifies a named action that is a parameterizable block of multiple top-level expressions.

### Syntax

1. `DEFINE ACTION`: action definition.
1. [Action name](https://ydb.tech/docs/en/yql/reference/syntax/expressions.md?version=main#named-nodes) that will be used to access the defined action further in the query.
1. The values of parameter names are listed in parentheses.
1. `AS` keyword.
1. List of top-level expressions.
1. `END DEFINE`: The marker of the last expression inside the action.

One or more of the last parameters can be marked with a question mark `?` as optional. If they are omitted during the call, they will be assigned the `NULL` value.

## DO {#do}

Executes an `ACTION` with the specified parameters.

### Syntax

1. `DO`: Executing an action.
1. The named expression for which the action is defined.
1. The values to be used as parameters are listed in parentheses.

`EMPTY_ACTION`: An action that does nothing.


### Example

```yql
DEFINE ACTION $hello_world($name, $suffix?) AS
    $name = $name ?? ($suffix ?? "world");
    SELECT "Hello, " || $name || "!";
END DEFINE;

DO EMPTY_ACTION();
DO $hello_world(NULL);
DO $hello_world("John");
DO $hello_world(NULL, "Earth");
```



## BEGIN .. END DO {#begin}

Performing an action without declaring it (anonymous action).

### Syntax

1. `BEGIN`.
1. List of top-level expressions.
1. `END DO`.

An anonymous action can't include any parameters.

### Example

```yql
DO BEGIN
    SELECT 1;
    SELECT 2 -- here and in the previous example, you might omit ';' before END
END DO
```