## TO_UPPER

The `TO_UPPER` function in ES|QL is used to convert an input string to upper case.

### Syntax

`TO_UPPER(str)`

#### Parameters

- `str`: This is a string expression. If null, the function returns null.

### Description

The function returns a new string representing the input string converted to upper case.

### Examples

Here are a couple of examples of full ES|QL queries using the `TO_UPPER` function:

```esql
ROW message = "Hello World"
| EVAL upper_message = TO_UPPER(message)
```

In this example, the `TO_UPPER` function is used to convert the string "Hello World" to upper case.

```esql
FROM employees
| EVAL upper_last_name = TO_UPPER(last_name)
| KEEP emp_no, upper_last_name
```

In this example, the `TO_UPPER` function is used to convert the `last_name` field of each record in the `employees` index to upper case. The query then keeps the `emp_no` and the upper case `last_name` for each record.