sql - 设置要在多个 SQL 选择查询中使用的条件

Question

需要设置运行多个查询的条件，但只想更改一次。例如，要设置年份、期间、文档，以便...

select * from tbl1 where tbl1.yr = year and ...
select * from tbl2 where tbl2.yr = year, and ...

Answer 1

创建视图：

CREATE VIEW yourview AS
SELECT * from tbl1
UNION ALL
SELECT * from tbl2

然后查询它：

 SELECT * FROM yourview
 WHERE tbl1.yr = year AND ...

您可能还想知道每行来自哪个表。这可以通过在视图中添加一个额外的列来实现：

CREATE VIEW yourview AS
SELECT 'tbl1' AS src, * from tbl1
UNION ALL
SELECT 'tbl2' AS src, * from tbl2

Answer 2

与CTE; 注意：你应该有same number of columns and matching datatypes from both tables，因为你正在做一个盲人union of select *

;with cte (myYear)
as (
   select @year as myYear
)
select * from table1 t1 where t1.year  in (select myYear from cte)
union all
select * from table2 t2 where t2.year  in (select myYear from cte)

Answer 3

如果它们是真正不同的查询，不相关，您可能不得不求助于动态 SQL，例如

DECLARE @sCondition VARCHAR(50)

SET @sCondition = 'yr = 2012'

DECLARE @sQuery1 VARCHAR(1000)

SET @sQuery1 = 'select * from tbl1 where ' + @sCondition

-- DECLARE other queries in similar faction OR combine multiple queries into single variable

EXEC (@sQuery1)