Oracle calculates day of the week based on date

in the work, the statements in the stored procedure are simply noted:       /**       determine the day of the week       */           Select Decode (To_char (To_date (iv_date,' Yyyy-mm-dd ') ), ' Monday ', ' 1 ', ' Tuesday ', ' 2 ', ' Wednesday ', ' 3 ', ' Thursday ', ' 4 ', ' Friday ', ' 5 ', ' Saturday ', ' 6 ', ' 7 ') into the      vi_weeknum from      dual       ; /**       calculates the date      of the last Monday from the input date */           Select To_char (to_date (iv_date,' Yyyy-mm-dd ')-(vi_weeknum-1)), ' YYYYMMDD ') into the      vi_week_monday from      dual;

Oracle calculates day of the week based on date