sql - 如何在视图中重用计算字段的结果

Question

我有一个这样构造的视图：

CREATE VIEW [dbo].[myview] AS
SELECT   
       dbo.table1.field1
      ,dbo.table2.field2  
      ,dbo.HeavyStoredProcedure(dbo.table1.field1) AS calculated_value 
      ...
FROM
      table1
      INNER JOIN table2 ON (...)
WHERE  
      ...
      AND NOT( EXISTS (SELECT * from table3 
               WHERE (table3.somefield = dbo.HeavyStoredProcedure(dbo.table1.field1)))
               OR
               EXISTS (SELECT * from table4
               WHERE (table4.anotherfield = dbo.HeavyStoredProcedure(dbo.table1.field1)))
             )

这里的问题是“HeavyStoredProcedure”被多次调用，参数完全相同，从而减慢了整个过程的速度。

如何让我的视图只在 table1 中的每行调用一次“HeavyStoredProcedure”，然后在 WHERE 子句中重复使用计算结果两次？

Answer 1

对于 SQL Server 试试这个：

CREATE VIEW [dbo].[myview] AS
SELECT   
       dbo.table1.field1
      ,dbo.table2.field2  
      ,
      ...
FROM
      table1
      INNER JOIN table2 ON (...)
      outer apply (
          select dbo.HeavyStoredProcedure(dbo.table1.field1) AS calculated_value 
      ) as CALC
WHERE  
      ...
      AND NOT( EXISTS (SELECT * from table3 
               WHERE (table3.somefield = CALC.calculated_value))
               OR
               EXISTS (SELECT * from table4
               WHERE (table4.anotherfield = CALC.calculated_value))
             )