string literal soql date format

Select * from case where WHERE CreatedDate = LAST_N_DAYS:30

//Date only:	
YYYY-MM-DD	1999-01-01

//Date, time, and time zone offset: YYYY-MM-DDThh:mm:ss+hh:mm
YYYY-MM-DDThh:mm:ss-hh:mm
YYYY-MM-DDThh:mm:ssZ
1999-01-01T23:01:01+01:00
1999-01-01T23:01:01-08:00
1999-01-01T23:01:01Z

delete [SELECT Id FROM Opportunity WHERE CreatedDate = LAST_YEAR];