---
layout: global
title: DECLARE VARIABLE
displayTitle: DECLARE VARIABLE
license: |
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  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at
 
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---

### Description

The `DECLARE VARIABLE` statement is used to create a temporary variable in Spark.
Temporary variables are scoped at a session level.

You can reference variables by their name everywhere constant expressions are allowed.
Unless you qualify a variable with `session` or `system.session`, a variable is only resolved after
Spark fails to resolve a name to a column or column alias.

Temporary variables cannot be referenced in persisted objects such as persisted view,
column default expressions, and generated column expressions.

### Syntax

```sql
DECLARE [ OR REPLACE ] [ VARIABLE ]
    variable_name [ data_type ] [ { DEFAULT | = } default_expr ]
```

### Parameters

* **OR REPLACE**

    If specified, a pre-existing temporary variable is replaced if it exists.

* **variable_name**

    Specifies a name for the variable to be created.
    The variable name may be optionally qualified with a `system`.`session` or `session`.

    **Syntax:** `[ system . [ session .] ] variable_name`

* **data_type**

    Optionally defines the data type of the variable.
    If it is not specified the type is derived from the default expression.

* **default_expr**

    An optional expression used to initialize the value of the variable after declaration.
    The expression is re-evaluated whenever the variable is reset to `DEFAULT` using
    [SET VAR](sql-ref-syntax-aux-set-var.html).
    If `data_type` is specified `default_expr` must be castable to the variable type.
    If `data_type` is not specified you must specify a default and its type will become the type of
    the variable.
    If no default expression is given, the variable is initialized with `NULL`.

### Examples

```sql
-- The dense form of declaring a variable with default
DECLARE five = 5;

-- STRING variable initialialized to `NULL`
DECLARE some_var STRING;
```

### Related Statements

* [DROP TEMPORARY VARIABLE](sql-ref-syntax-ddl-drop-variable.html)
* [SET VARIABLE](sql-ref-syntax-aux-set-var.html)