FIRST_DAY

The FIRST_DAY function returns a date or timestamp that represents the first day of the month indicated by expression.

expression: An expression that returns a value of one of the following built-in data types: a date, a timestamp, a character string, or a graphic string.
If expression is a character or graphic string, its value must be a valid string representation of a date or timestamp. For the valid formats of string representations of dates and timestamps, see String representations of datetime values.

The result of the function has the same data type as expression, unless expression is a string in which case the result is DATE. If the argument can be null, the result can be null; if the argument is null, the result is the null value.

Any hours, minutes, seconds, or fractional seconds information included in expression is not changed by the function.

Example

Set the host variable FIRST_OF_MONTH with the first day of the current month.
```
SET :FIRST_OF_MONTH = FIRST_DAY(CURRENT_DATE)
```
The host variable FIRST_OF_MONTH is set with the value representing the beginning of the current month. If the current day is 2000-02-10, then FIRST_OF_MONTH is set to 2000-02-01.
Set the host variable FIRST_OF_MONTH with the first day of the month in European standard format for the given date.
```
SET :FIRST_OF_MONTH = CHAR(FIRST_DAY(DATE '1965-07-07'), EUR)
```
The host variable FIRST_OF_MONTH is set with the value '01.07.1965'.