NLS_LOWER converts all alphabetic characters in a text expression to lowercase. The data type of the return value is the same as the original text.
CHAR | NCHAR | VARCHAR2 | NVARCHAR2
NLS_LOWER (char [, 'nlsparam' ])
char can be any text expression.
nlsparam is a linguistic sort sequence in the form NLS_SORT =sort[_ai |_ci], where sort is an NLS language. You can add a suffix to the language to modify the sort: _ai for an accent-insensitive sort, or _ci for a case-insensitive sort.
NLS_LOWER('STOP SHOUTING') returns the string stop shouting.