Hive Case When与IF的用法（嵌套、混合使用）_hive select case when

1、CASE WHEN

1.1、CASE WHEN 语法

case when 条件表达式 
  then 条件成立，结果1 
  else 条件不成立，结果2 
end
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1.2、单个条件

1.2.1、CASE WHEN … THEN … END 结构

如果不写ELSE，那么除了符合WHEN** **条件之外的数据，其他数据默认为NULL

spark-sql> select 
         >   user_id,
         >   name,
         >   case when address='shanghai' then '上海' end as address
         > from test.test8;
1    xiaoming    上海
2    xiaolan     NULL
Time taken: 0.219 seconds, Fetched 2 row(s)
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1.2.2、case when…then…else…end 结构

spark-sql> select 
         >   user_id,
         >   name,
         >   case when address='shanghai' then '上海' else '其他' end as address
         > from test.test8;
1    xiaoming    上海
2    xiaolan     其他
Time taken: 0.396 seconds, Fetched 2 row(s)
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1.3、多个条件

1.3.1、CASE WHEN … THEN … WHEN … THEN … ELSE END 结构

spark-sql> select 
         >   user_id,
         >   name,
         >   case when address='shanghai' then '上海' 
         >        when address='beijing' then '北京'
         >        else '其他'
         >   end as address
         > from test.test8;
1    xiaoming     上海                                                    
2    xiaolan      北京
Time taken: 4.57 seconds, Fetched 2 row(s)
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1.3.2、CASE WHEN嵌套结构

case when…then…case when…then…else…end when…then…case when…then…else…end else…end结构：

spark-sql> select 
         >   user_id,
         >   name,
         >   case 
         >     when name='xiaoming' 
         >       then 
         >         case when address='shanghai' then '上海' else '其他' end 
         >     when name='xiaolan'
         >       then
         >         case when address='beijing' then '北京' else '其他' end 
         >   else '其他' end as address
         > from test.test8;
1    xiaoming    上海                                                    
2    xiaolan     北京
3    xiaohong    其他
Time taken: 1.072 seconds, Fetched 3 row(s)
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2、IF语法

2.1、IF语法

if（条件表达式，条件成立-结果1，条件不成立-结果2）
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2.2、单个条件

if(条件，结果1，结果2)结构：

spark-sql> select 
         >   user_id,
         >   name,
         >   address,
         >   if(address='shanghai','上海','其他') as address_name
         > from test.test8;
1    xiaoming    shanghai     上海                                    
2    xiaolan     beijing      其他
3    xiaohong    guangzhou    其他
Time taken: 11.957 seconds, Fetched 3 row(s)
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2.3、多个条件

2.3.1、IF嵌套结构

if(if(条件, 结果1, 结果2), 结果1, 结果2)

spark-sql> select 
         >   user_id,
         >   name,
         >   address,
         >   if(name='xiaoming',if(address='shanghai','上海','其他'),'其他') as address_name
         > from test.test8;
1    xiaoming    shanghai     上海                                    
2    xiaolan     beijing      其他
3    xiaohong    guangzhou    其他
Time taken: 5.452 seconds, Fetched 3 row(s)
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2.3.2、IF和CASE WHEN混合使用

if(条件, case when…then…end, 结果2)结构

spark-sql> select 
         >   user_id,
         >   name,
         >   address,
         >   if(name='xiaoming',
         >   case when address='shanghai' then '上海' else '其他' end,
         >   '其他') as address_name
         > from test.test8;
1    xiaoming     shanghai    上海                                    
2    xiaolan      beijing     其他
3    xiaohong    guangzhou    其他
Time taken: 12.791 seconds, Fetched 3 row(s)
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