Question

因此，这里的MAX用于数据透视表的用途是什么，没有它，查询将无法进行。

// We get the assembly through the base class
var baseAssembly = typeof(baseClass).GetTypeInfo().Assembly;

// we filter the defined classes according to the interfaces they implement
var typeList = baseAssembly.DefinedTypes.Where(type => type.ImplementedInterfaces.Any(inter => inter == typeof(IMyInterface))).ToList();

Answer 1

使用聚合函数可以减少行数，从而将单个（伪）聚合行中每个值的结果压缩为

您还可以使用min或其他聚合函数，该函数的用途仅是将多行减少为一并获得数据透视结果

SELECT
  item_id,
  MIN(IF(property_name = 'color', value, NULL)) AS color,
  MIN(IF(property_name = 'size', value, NULL)) AS size,
  MIN(IF(property_name = 'weight', value, NULL)) AS weight
FROM
  properties
GROUP BY
  item_id

在此查询中解释Max

1 个答案: