选择一列 DISTINCT SQL

2022-01-09 00:00:00 sql sql-server coldfusion cfml

添加:使用 SQL Server 2000 和 2005，因此必须同时处理这两个版本.另外，value_rk 不是数字/整数(错误:操作数数据类型 uniqueidentifier 对 min 运算符无效)

Added: Working with SQL Server 2000 and 2005, so has to work on both. Also, value_rk is not a number/integer (Error: Operand data type uniqueidentifier is invalid for min operator)

当我不关心返回的其他列时，有没有办法进行单列DISTINCT"匹配?示例:

Is there a way to do a single column "DISTINCT" match when I don't care about the other columns returned? Example:

**Table**
Value A, Value L, Value P
Value A, Value Q, Value Z

我只需要根据第一行(值 A)中的内容返回这些行中的一个.我仍然需要第二列和第三列的结果(无论如何，第二列实际上应该完全匹配，但第三列是唯一键，我至少需要其中一个).

I need to return only one of these rows based on what is in the first one (Value A). I still need results from the second and third columns (the second should actually match all across the board anyway, but the third is a unique key, which I need at least one of).

这是我到目前为止所得到的，虽然它显然不起作用:

Here's what I've got so far, although it doesn't work obviously:

SELECT value, attribute_definition_id, value_rk
FROM attribute_values
WHERE value IN (
    SELECT value, max(value_rk)
    FROM attribute_values
)
ORDER BY attribute_definition_id

我在 ColdFusion 工作，所以如果有一个简单的解决方法，我也愿意接受.我试图限制或分组"第一列值".value_rk 是我的大问题，因为每个值都是唯一的，但我只需要一个.

I'm working in ColdFusion so if there's a simple workaround in that I'm open to that as well. I'm trying to limit or "group by" the first column "value". value_rk is my big problem since every value is unique but I only need one.

注意:value_rk 不是数字，因此这不起作用

NOTE: value_rk is not a number, hence this DOES NOT WORK

更新:我有一个工作版本，它可能比纯 SQL 版本慢很多，但老实说，在这一点上任何工作都比没有好.它从第一个查询中获取结果，执行第二个查询，除了将结果限制为一个，并为匹配的值获取匹配的 value_rk.像这样:

UPDATE: I've got a working version, it's probably quite a bit slower than a pure SQL version, but honestly anything working at this point is better than nothing. It takes the results from the first query, does a second query except limiting it's results to one, and grabs a matching value_rk for the value that matches. Like so:

<cfquery name="queryBaseValues" datasource="XXX" timeout="999">
    SELECT DISTINCT value, attribute_definition_id
    FROM attribute_values
    ORDER BY attribute_definition_id
</cfquery>

<cfoutput query="queryBaseValues">
    <cfquery name="queryRKValue" datasource="XXX">
        SELECT TOP 1 value_rk
        FROM attribute_values
        WHERE value = '#queryBaseValues.value#'
    </cfquery>
    <cfset resourceKey = queryRKValue.value_rk>
    ...

这样就完成了，在 ColdFusion 中明确地选择了一个列.仍然非常欢迎任何纯 SQL Server 2000/2005 建议:)

So there you have it, selecting a single column distinctly in ColdFusion. Any pure SQL Server 2000/2005 suggestions are still very welcome :)

推荐答案

这可能有效:

SELECT DISTINCT a.value, a.attribute_definition_id, 
  (SELECT TOP 1 value_rk FROM attribute_values WHERE value = a.value) as value_rk
FROM attribute_values as a
ORDER BY attribute_definition_id

.. 未测试.

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