sql中条件判断的语句如何写啊 If 后不用大括号的啊不知哪错了小弟我急_Sql Server

sql中条件判断的语句怎么写啊 If 后不用大括号的啊，不知哪错了我急！！求救！！
Select top 5 vol_ArcType,vol_QZH,Vol_DH,Vol_AJBT,Vol_YS,Vol_BGQX,
(
if (charindex('-',Vol_Date)>0)
begin
case
when len( substring(Vol_Date,1,charindex('-',Vol_Date)-1))=4 then convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1)+'.01.01',120)
when len( substring(Vol_Date,1,charindex('-',Vol_Date)-1))=7 then convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1)+'.01',120)
else convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1),120)
end
end
if (charindex('-',Vol_Date)<1)
begin
case
when len(Vol_Date)=4 then convert(datetime,Vol_Date+'.01.01',120)
when len(Vol_Date)=7 then convert(datetime,Vol_Date+'.01',120)
else convert(datetime,Vol_Date,120)
end
end
) as Vol_BZQSRQ From Table

消息 156，级别 15，状态 1，第 7 行
关键字 'if' 附近有语法错误。
消息 156，级别 15，状态 1，第 9 行
关键字 'case' 附近有语法错误。
消息 156，级别 15，状态 1，第 17 行
关键字 'case' 附近有语法错误。
哪里错了啊！

------解决方案--------------------

SQL code

Select  top 5 vol_ArcType,vol_QZH,Vol_DH,Vol_AJBT,Vol_YS,Vol_BGQX, (        case when charindex('-',Vol_Date)>0         then          case             when len( substring(Vol_Date,1,charindex('-',Vol_Date)-1))=4 then convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1)+'.01.01',120)             when len( substring(Vol_Date,1,charindex('-',Vol_Date)-1))=7 then convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1)+'.01',120)             else convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1),120)                      when charindex('-',Vol_Date) <1     then         case             when len(Vol_Date)=4 then convert(datetime,Vol_Date+'.01.01',120)             when len(Vol_Date)=7 then convert(datetime,Vol_Date+'.01',120)             else convert(datetime,Vol_Date,120)                 end   ) as Vol_BZQSRQ From Table
------解决方案--------------------
SQL code这样试试Select  top 5 vol_ArcType,vol_QZH,Vol_DH,Vol_AJBT,Vol_YS,Vol_BGQX, ( case       when (charindex('-',Vol_Date)>0) then                 case             when len( substring(Vol_Date,1,charindex('-',Vol_Date)-1))=4 then convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1)+'.01.01',120)             when len( substring(Vol_Date,1,charindex('-',Vol_Date)-1))=7 then convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1)+'.01',120)             else convert(datetime, substring(Vol_Date,1,charindex('-',Vol_Date)-1),120)           end            when (charindex('-',Vol_Date) <1) then               case             when len(Vol_Date)=4 then convert(datetime,Vol_Date+'.01.01',120)             when len(Vol_Date)=7 then convert(datetime,Vol_Date+'.01',120)             else convert(datetime,Vol_Date,120)           end          end) as Vol_BZQSRQ From Table