# NVL and COALESCE functions
<a name="NVL_function"></a>

Returns the value of the first expression that isn't null in a series of expressions. When a non-null value is found, the remaining expressions in the list aren't evaluated. 

NVL is identical to COALESCE. They are synonyms. This topic explains the syntax and contains examples for both.

## Syntax
<a name="NVL_function-synopsis"></a>

```
NVL( expression, expression, ... )
```

The syntax for COALESCE is the same:

```
COALESCE( expression, expression, ... )
```

If all expressions are null, the result is null.

These functions are useful when you want to return a secondary value when a primary value is missing or null. For example, a query might return the first of three available phone numbers: cell, home, or work. The order of the expressions in the function determines the order of evaluation.

## Arguments
<a name="NVL_function-arguments"></a>

 *expression*   
An expression, such as a column name, to be evaluated for null status.

## Return type
<a name="NVL_function-returntype"></a>

AWS Clean Rooms determines the data type of the returned value based on the input expressions. If the data types of the input expressions don't have a common type, then an error is returned.

## Examples
<a name="NVL_function-examples"></a>

If the list contains integer expressions, the function returns an integer. 

```
SELECT COALESCE(NULL, 12, NULL);

coalesce
--------------
12
```

This example, which is the same as the previous example, except that it uses NVL, returns the same result. 

```
SELECT NVL(NULL, 12, NULL);

coalesce
--------------
12
```

The following example returns a string type.

```
SELECT COALESCE(NULL, 'AWS Clean Rooms', NULL);

coalesce
--------------
AWS Clean Rooms
```

The following example results in an error because the data types vary in the expression list. In this case, there is both a string type and a number type in the list.

```
SELECT COALESCE(NULL, 'AWS Clean Rooms', 12);
ERROR: invalid input syntax for integer: "AWS Clean Rooms"
```