Question

我们正在做这样的事情

create view v1 
as 
select 'tab1' as table_name , * from table1
union All
select 'tab2' as table_name , * from table2
union All
select 'tab3' as table_name , * from table3

然后在SP中，

declare @var = function_gettablename()
    select * from v1 where table_name = @var and datetoload = <ActualDate>

function_gettablename() = gives the table name based on parameters

datetoload =非聚集索引列，在所有表上都是mutuallt独占。即一个日期仅在一个表格中可用

现在问题在于执行计划：使用@var使视图查询所有三个表而不是所需的表。

有没有办法应用过滤器然后应用union all，而不是运行union all然后应用过滤器。

由于 AB

Answer 1

请检查一下 - ：

DECLARE @Var VARCHAR(MAX)
SET @Var = function_gettablename()
DECLARE @Sql VARCHAR(MAX)
DECLARE @ActualDate DATETIME
SET @ActualDate ='2013/2/14'

SET @sql = 'SELECT tab1 as '+@Var+' , * FROM table1 
            WHERE dateload ='+@ActualDate+ ' UNION ALL
            SELECT tab2 as '+@Var+' , * FROM table1 
            WHERE dateload ='+@ActualDate+' UNION ALL
            SELECT tab3 as '+@Var+',* FROM table1 
            WHERE dateload ='+@ActualDate

Exec(@Sql)

避免查看多个表，在不需要时查询所有表

1 个答案: