在 C# 中是这样的:
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:
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。
最佳答案
我的回答仅基于您帖子的标题,因为我不懂 C#,也不理解给定的查询。但在 MySQL 中,我建议您尝试子选择。首先获取一组感兴趣列的主键,然后从这些行中选择数据:
SELECT somecolumn, anothercolumn
FROM sometable
WHERE id IN (
SELECT min(id)
FROM sometable
GROUP BY somecolumn
);
关于mysql - 如何为 MySQL 中的每个组选择第一行?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/2739474/