计算列-在关键字'when‘附近的不正确语法

Question

我正在尝试向SQLServer2008Express表中添加计算列。

公式是：

case when callrecord_contacttype=1 then 'Routed voice' 
else when callrecord_contacttype=2 then 'Direct incoming voice' 
else when callrecord_contacttype=3 then 'Direct outgoing voice' 
else when callrecord_contacttype=4 then 'Direct internal voice' 
else when callrecord_contacttype=5 then 'Routed callback' 
else when callrecord_contacttype=6 then 'Routed email' 
else when callrecord_contacttype=7 then 'Direct outgoing email' 
else when callrecord_contacttype=8 then 'Routed chat' else '' end

但我发现了错误：

在关键字'when‘附近有错误的语法。

Answer 1

试着：

case callrecord_contacttype
    when 1 then 'Routed voice' 
    when 2 then 'Direct incoming voice' 
    when 3 then 'Direct outgoing voice' 
    when 4 then 'Direct internal voice' 
    when 5 then 'Routed callback' 
    when 6 then 'Routed email' 
    when 7 then 'Direct outgoing email' 
    when 8 then 'Routed chat'
    else ''
end

有关语法，请参见http://msdn.microsoft.com/en-us/library/ms181765.aspx。

Answer 2

查询中只有一个ELSE：

case when callrecord_contacttype=1 then 'Routed voice' 
when callrecord_contacttype=2 then 'Direct incoming voice' 
when callrecord_contacttype=3 then 'Direct outgoing voice' 
when callrecord_contacttype=4 then 'Direct internal voice' 
when callrecord_contacttype=5 then 'Routed callback' 
when callrecord_contacttype=6 then 'Routed email' 
when callrecord_contacttype=7 then 'Direct outgoing email' 
when callrecord_contacttype=8 then 'Routed chat' 
else '' end

Answer 3

else只属于最后的非条件子句：

case when callrecord_contacttype=1 then 'Routed voice' 
     when callrecord_contacttype=2 then 'Direct incoming voice' 
     when callrecord_contacttype=3 then 'Direct outgoing voice' 
     when callrecord_contacttype=4 then 'Direct internal voice' 
     when callrecord_contacttype=5 then 'Routed callback' 
     when callrecord_contacttype=6 then 'Routed email' 
     when callrecord_contacttype=7 then 'Direct outgoing email' 
     when callrecord_contacttype=8 then 'Routed chat'
     else '' end