Oracle update select

UPDATE 
   GSMRSTATISTICS G
 SET
   (G.BSCMONTHAVG_, 
   G.BSCMONTHMAX_) = 
   ( SELECT 
     AVG(B.CPUOCCUPANCYAVG_) "BSC主处理器月平均负荷",
     MAX(B.CPUOCCUPANCYMAX_) "BSC主处理器月峰值负荷"
     FROM 
       BSCCPUBURDEN B
     WHERE 
       B.GSMRSTATISTICS_ID = '1')
 WHERE G.ID_ = '1'