Question

我有这样的查询：

（如您所见，我想检索总行数的50％或前100行等）

//@AllRowsSelectType is INT

 SELECT TOP (
    case @AllRowsSelectType
        when 1 then 100 PERCENT 
        when 2 then 50 PERCENT
        when 3 then 25 PERCENT
        when 4 then 33 PERCENT
        when 5 then 50
        when 6 then 100
        when 7 then 200 
    end
            ) ROW_NUMBER() OVER(ORDER BY [id]) AS row_num, a,b,c etc

为什么我会出现错误：“关键字'PERCENT'附近的语法不正确。”就行“当1 [...]”时

Answer 1

TOP的语法是：

TOP (expression) [PERCENT]
[ WITH TIES ]

reserved keyword PERCENT不能包含在表达式中。相反，您可以运行两个不同的查询：一个用于何时需要PERCENT，另一个用于不需要时。

如果您需要将此作为一个查询，则可以运行两个查询并使用UNION ALL来组合结果：

SELECT TOP (
    CASE @AllRowsSelectType
        WHEN 1 THEN 100
        WHEN 2 THEN 50
        WHEN 3 THEN 25
        WHEN 4 THEN 33 
        ELSE 0
    END) PERCENT
    ROW_NUMBER() OVER(ORDER BY [id]) AS row_num, a, b, c, ...
UNION ALL
SELECT TOP (
    CASE @AllRowsSelectType
        WHEN 5 THEN 50
        WHEN 6 THEN 100
        WHEN 7 THEN 200
        ELSE 0
    END)
    ROW_NUMBER() OVER(ORDER BY [id]) AS row_num, a, b, c, ...

Answer 2

您还混合了两种不同类型的用途。另一个是。

DECLARE @ROW_LIMT int

IF @AllRowsSelectType < 5
    SELECT @ROW_LIMIT = COUNT(*)/@AllRowsSelectType FROM myTable -- 100%, 50%, 33%, 25%
ELSE
    SELECT @ROW_LIMIT = 50 * POWER(2, @AllRowsSelectType - 5) -- 50, 100, 200...

WITH OrderedMyTable
(
  select *, ROW_NUMBER() OVER (ORDER BY id) as rowNum
  FROM myTable
)
SELECT * FROM OrderedMyTable
WHERE rowNum <= @ROW_LIMIT

Answer 3

你可以这样做：

select top (CASE @FilterType WHEN 2 THEN 50 WHEN 3 THEN 25 WHEN 4 THEN 33 ELSE 100 END) percent * from
(select top (CASE @FilterType WHEN 5 THEN 50 WHEN 6 THEN 100 WHEN 7 THEN 200 ELSE 2147483647 END) * from
<your query here>
) t
) t

这可能更容易阅读。

T-SQL SELECT TOP的问题（案例[...]）

3 个答案: