Q55411598, Oracle - rextester

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with a(ALIAS, LEVEL_20, POINTS, "DATE") as
    (
     select 'Jbax',300,325,date'2018-06-20' from dual union all
     select 'Cvg2',100,103,date'2018-06-20' from dual union all
     select 'Deg1',200,281,date'2018-06-20' from dual         
    ),   b(ALIAS, CODE_LEVEL, PRIZE, "DATE") as
    (
     select 'Jbax','Level_20',500,date'2017-01-15' from dual union all
     select 'Jbax','Level_10',200,date'2017-03-20' from dual union all
     select 'Cvg2','Level_20',100,date'2017-04-05' from dual union all
     select 'Deg1',null,null,null  from dual union all    
     select 'Cvg2','Level_20',50,date'2017-02-01'  from dual
    ),   c(ALIAS,NAME) as
    (
     select 'Jbax','Jessie' from dual union all 
     select 'Cvg2','Carol' from dual union all
     select 'Deg1','Danny' from dual
    )  
    select c.name, a.level_20
      from c
      join a on a.alias = c.alias  
     where (a.alias,a.level_20) not in 
          (select a.alias,b.prize 
             from a
             join b on b.prize = a.level_20 and b.code_level = 'Level_20')


absolute service time: 1,09 sec