本文介绍了如何在MySQL中为每个组选择第一行?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着跟版网的小编来一起学习吧！
问题描述
在 C# 中是这样的:
In C# it would be like this:
table
.GroupBy(row => row.SomeColumn)
.Select(group => group
.OrderBy(row => row.AnotherColumn)
.First()
)
Linq-To-Sql 将其转换为以下 T-SQL 代码:
Linq-To-Sql translates it to the following T-SQL code:
SELECT [t3].[AnotherColumn], [t3].[SomeColumn]
FROM (
SELECT [t0].[SomeColumn]
FROM [Table] AS [t0]
GROUP BY [t0].[SomeColumn]
) AS [t1]
OUTER APPLY (
SELECT TOP (1) [t2].[AnotherColumn], [t2].[SomeColumn]
FROM [Table] AS [t2]
WHERE (([t1].[SomeColumn] IS NULL) AND ([t2].[SomeColumn] IS NULL))
OR (([t1].[SomeColumn] IS NOT NULL) AND ([t2].[SomeColumn] IS NOT NULL)
AND ([t1].[SomeColumn] = [t2].[SomeColumn]))
ORDER BY [t2].[AnotherColumn]
) AS [t3]
ORDER BY [t3].[AnotherColumn]
但它与 MySQL 不兼容.
But it is incompatible with MySQL.
推荐答案
当我写作时
SELECT AnotherColumn
FROM Table
GROUP BY SomeColumn
;
它有效.IIRC 在其他 RDBMS 这样的语句中是不可能的，因为不属于分组键的列被引用而没有任何类型的聚合.
It works. IIRC in other RDBMS such statement is impossible, because a column that doesn't belongs to the grouping key is being referenced without any sort of aggregation.
这种怪癖"与我想要的非常接近.所以我用它来得到我想要的结果:
This "quirk" behaves very closely to what I want. So I used it to get the result I wanted:
SELECT * FROM
(
SELECT * FROM `table`
ORDER BY AnotherColumn
) t1
GROUP BY SomeColumn
;
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