Question

我想使用DB2实现这种类型的逻辑：

Create Procedure sp_MyProcedure (
    IN Var1 Decimal(6, 0),
    IN Var2 Decimal(6, 0)
) Language SQL

Dynamic Result Sets 1

Begin

If Exists(Select * from MyTable where CustomerNbr = Var1) Then

    return (Select * from MyTable where CustomerNbr = Var1)

Else If Exists(Select * from MyTable where CustomerNbr = Var2) Then

    return (Select * from MyTable where CustomerNbr = Var2)

Else

    return (Select * from MyTable where CustomerNbr = 0)

End If

End

但无法弄清楚实现此类逻辑的语法。另外，我每次运行两次查询;一次检查它是否返回值，如果确实返回值，则一次创建返回的数据集。所以，我知道必须有更好的方法。我一直在查看“With”语句来创建临时表，但到目前为止，它基本上存在效率低下和语法限制相同的问题。

（我为代码的格式化道歉。我似乎无法让它在这个文本编辑器中正常工作）有人可以建议最好的方法来实现这一目标吗？提前谢谢您的建议。

Answer 1

这是一个丑陋的select语句：

With allrecords as
(
  Select 1 as qnum,* 
  from MyTable 
  where CustomerNbr = Var1
  union all 
  Select 2 as qnum, *
  from MyTable
  where CustomerNbr = Var2
  union all
  Select 3 as qnum, * 
  from MyTable 
  where CustomerNbr = 0
)
select *
from allrecords
where qnum = (select min(qnum) from allrecords)

注意，如果你不想在结果中返回qnum，那么你必须为不包含qnum的最终select语句提供一个选择列表。

Answer 2

我能想到的最好是：

SELECT * FROM MyTable
WHERE custNo = Var1
OR (custNo != Var1
AND custNo = Var2)
OR (custNo != Var1
AND custNo != Var2
AND custNo = 0);

Answer 3

如果有人工作，你想要排除其他人。怎么样？

with A as
(select *
   from mytable
   where customer = var1
), Ax as
(select count(*) as tally
   from a
), B as
(select * 
   from mytable, Ax
   where Ax.tally = 0
     and customer = var2 
), Bx as
(select count(*) as tally
   from B
), C as
(select *
   from mytable, Ax, Bx
   where Ax.tally=0
     and Bx.tally=0
     and Customer=0
)
select * from A
UNION
select * from B
UNION
select * from C

选择在DB2中返回结果的第一个查询的最佳方法是什么

3 个答案: