Question

我必须将一个参数传递给一个条件来选择行，如果我传递0它应该选择所有行，1 - 只有HDD，2 - 除硬盘外的所有行

请参阅代码：

declare @Accessories table (id int, name nvarchar(20), atype nvarchar(20), itype int)

insert into @Accessories values (1, 'Seagate HDD 100GB', 'HDD', 1)
insert into @Accessories values (2, 'Samsung HDD 100GB', 'HDD', 1)
insert into @Accessories values (3, 'WD HDD 500GB', 'HDD', 1)
insert into @Accessories values (4, 'Samsung 4GB', 'RAM', 2)
insert into @Accessories values (5, 'GeForce 512MB', 'Video', 3)

declare @param int

set @param = 1 /* 0 - All records, 1 - Only HDD, 2 - All exclude HDD */

select 
    * 
from @Accessories
where itype = @param /* NEED RIGHT CONDITION HERE*/

我不能像@param = 0那样编写代码然后...... 是否可以在WHERE语句中写入条件？

谢谢！

Answer 1

您可以使用以下内容：

select * 
from @Accessories 
where (@Param = 0)
  or (@Param = 1 and atype = 'HDD') 
--or (@Param = 1 and itype = 1) , if itype and atype are connected
  or (@Param = 2 and atype != 'HDD')
option (recompile)

如果Param为0，则第一个条件变为0=0并匹配所有行，因此返回所有行。如果param为1或2，则只有相应或分支在第一个条件上匹配，因此它返回第二个条件指定的内容。

此外，option (recompile)非常重要（查看Martin评论中的文章）。它指示SQL Server在准备执行计划时使用参数的运行时值，基本上是这样的：

当@Param = 0时，查询变为select * from @Accessories
当@Param = 1时，查询变为select * from @Accessories where atype = 'HDD'
当@Param = 2时，查询变为select * from @Accessories where atype != 'HDD'

Answer 2

WHERE itype BETWEEN @param AND CASE 
    WHEN @param = 1 THEN 1
    ELSE 2000000000 END
OPTION (RECOMPILE); -- thanks for the reminder @Martin

Answer 3

declare @Accessories table (id int, name nvarchar(20), atype nvarchar(20))

insert into @Accessories values (1, 'Seagate HDD 100GB', 'HDD')
insert into @Accessories values (2, 'Samsung HDD 100GB', 'HDD')
insert into @Accessories values (3, 'WD HDD 500GB', 'HDD')
insert into @Accessories values (4, 'Samsung 4GB', 'RAM')
insert into @Accessories values (5, 'GeForce 512MB', 'Video')

declare @param int

set @param = 0 /* 0 - All records, 1 - Only HDD, 2 - All exclude HDD */

if(@param =0)
begin
select * from @Accessories
end
if(@param =1)
begin
select * from @Accessories where atype in ('HDD')
end
if(@param =2)
begin
select * from @Accessories where atype not in('HDD')
end

WHERE子句中的多个条件

3 个答案: