_first_of_month
Returns a date or datetime, depending on the argument, by converting "date_expression" to a date with the same year and month but with the day set to 1.
Syntax
_first_of_month ( date_expression )
Example 1
_first_of_month ( 2002-04-20 )
Result
2002-04-01
Example 2
_first_of_month ( 2002-04-20 12:10:10.000 )
Result
2002-04-01 12:10:10.000