if .. else .. create table variable

想要動依不同情況建立相同名稱的table variable,語法如下

 if @condition = '1'

begin

  declare @tmptable1 table (col1 int,col2 int)

end

else

begin

  declare @tmptable1 table (col1 int,col2 int, col3 int, col4 int)

end

出現以下錯誤
Msg 134, Level 15, State 1, Line 13
The variable name '@tmptable1' has already been declared. Variable names must be unique within a query batch or stored procedure.

改成用temp table 也不行

 if @condition = '1'

begin

    create table #tmptable1  (col1 int,col2 int)

end

else

begin

   create table #tmptable1  (col1 int,col2 int, col3 int, col4 int)

end


 出現以下錯誤
Msg 2714, Level 16, State 1, Line 15
There is already an object named '#tmptable1' in the database.

最後折衷好了...馬是口以啦...

 create table #tmptable1  (col1 int,col2 int, col3 int, col4 int)

 if @condition = '1'

begin

    alter table #tmptable1
    drop column col3,col4

end

ps. table variable 無法alter , 但用temp table又會有transaction log, 得要觀察performance看看