不拼接sql字符串实现多条件查询
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写法1：
if (@adddate is not null) and (@name <> '')
select * from table where adddate = @adddate and name = @name
else if (@adddate is not null) and (@name ='')
select * from table where adddate = @adddate
else if(@adddate is null) and (@name <> '')
select * from table where and name = @name
else if(@adddate is null) and (@name = '')
select * from table
写法2：
select * from table where (adddate = @adddate or @adddate is null) and (name = @name or @name = '')
写法3：
select * from table where
adddate = case @adddate is null then adddate else @adddate end,
name = case @name when '' then name else @name end
