R中sqldf中的聚合用例出错

我想识别源代码方面的流量，为此我需要使用case对不同的流量源进行分组。当有一种方法可以在R中实现时，我下面的代码抛出了错误

grouped_sources <- sqldf("SELECT 
       CASE WHEN First_Source_ = 'undefined' THEN 'Undefined'
       WHEN First_Source_ = ' Internet ' THEN 'Interner'
       WHEN First_Source_ = 'Friend' THEN 'Friend'
       WHEN First_Source_ IN ('Google','adwords','google') THEN 'Google'
       WHEN First_Source_ = 'Former Student' THEN 'Former Student'
       WHEN First_Source_ IN('Facebook','facebook') THEN 'Facebook'
       WHEN First_Source_ IS NULL THEN 'Null'
       ELSE 'Other' END CASE AS Source, COUNT(*) AS Count 
       FROM turnover 
       GROUP BY First_Source_,CASE WHEN First_Source_ = 'undefined' THEN 'Undefined'
       WHEN First_Source_ = ' Internet ' THEN 'Interner'
       WHEN First_Source_ = 'Friend' THEN 'Friend'
       WHEN First_Source_ IN ('Google','adwords','google') THEN 'Google'
       WHEN First_Source_ = 'Former Student' THEN 'Former Student'
       WHEN First_Source_ IN('Facebook','facebook') THEN 'Facebook'
       WHEN First_Source_ IS NULL THEN 'Null'
       ELSE 'Other'")

---

这会不断抛出错误：near CASE:syntax Error是指在R？？？中使用CASE时遇到类似问题的任何人，因为错误消息表明CASE语句没有正确的语法。它错过了结局