sql中的CASE;update

 select(case

             when instr(str,'/R')>0  then

             substr(str,1,instr(str,'/R')-1)

             when instr(str,'/T')>0 then

             substr(str,1,instr(str,'/T')-1)

             else

                   '0'

             end)

from table_name;

update:   update table_name set table_name.attribute=(嵌套查詢語句)