aggregation

Custom aggregate function (concat) in SQL Server

由 时光怂恿深爱的人放手 提交于 2019-11-26 11:09:46
问题 Question: I want to write a custom aggregate function that concatenates string on group by. So that I can do a SELECT SUM(FIELD1) as f1, MYCONCAT(FIELD2) as f2 FROM TABLE_XY GROUP BY FIELD1, FIELD2 All I find is SQL CRL aggregate functions, but I need SQL, without CLR. Edit:1 The query should look like this: SELECT SUM(FIELD1) as f1, MYCONCAT(FIELD2) as f2 FROM TABLE_XY GROUP BY FIELD0 Edit 2: It is true that it isn\'t possible without CLR. However, the subselect answer by astander can be

Aggregation in pandas

由 喜欢而已 提交于 2019-11-26 10:34:59
How to perform aggregation with pandas? No DataFrame after aggregation! What happened? How to aggregate mainly strings columns (to list s, tuple s, strings with separator )? How to aggregate counts? How to create new column filled by aggregated values? I've seen these recurring questions asking about various faces of the pandas aggregate functionality. Most of the information regarding aggregation and its various use cases today is fragmented across dozens of badly worded, unsearchable posts. The aim here is to collate some of the more important points for posterity. This Q/A is meant to be

UML aggregation vs association

由 不羁岁月 提交于 2019-11-26 09:07:12
问题 Here I am, with another question about aggregation and association. I wanted to learn some basics of UML, so I started reading \"UML distilled\" by Martin Fowler. I read both chapters about classes, and there is one thing that I can\'t fully grasp I think, and that is aggregation vs association. In the book there is this quote: In the pre-UML days, people were usually rather vague on what was aggregation and what was association. Whether vague or not, they were always inconsistent with

MySQL - Using COUNT(*) in the WHERE clause

由 半城伤御伤魂 提交于 2019-11-26 08:49:27
问题 I am trying to accomplish the following in MySQL (see pseudo code) SELECT DISTINCT gid FROM `gd` WHERE COUNT(*) > 10 ORDER BY lastupdated DESC Is there a way to do this without using a (SELECT...) in the WHERE clause because that would seem like a waste of resources. 回答1: try this; select gid from `gd` group by gid having count(*) > 10 order by lastupdated desc 回答2: I'm not sure about what you're trying to do... maybe something like SELECT gid, COUNT(*) AS num FROM gd GROUP BY gid HAVING num

Implementation difference between Aggregation and Composition in Java

由 笑着哭i 提交于 2019-11-26 04:57:38
问题 I\'m aware of the conceptual differences between Aggregation and Composition. Can someone tell me the implementation difference in Java between them with examples? 回答1: Composition final class Car { private final Engine engine; Car(EngineSpecs specs) { engine = new Engine(specs); } void move() { engine.work(); } } Aggregation final class Car { private Engine engine; void setEngine(Engine engine) { this.engine = engine; } void move() { if (engine != null) engine.work(); } } In the case of

Is there an Oracle SQL query that aggregates multiple rows into one row? [duplicate]

由 柔情痞子 提交于 2019-11-26 01:34:49
问题 This question already has an answer here: SQL Query to concatenate column values from multiple rows in Oracle 11 answers I have a table that looks like this: A 1 A 2 B 1 B 2 And I want to produce a result set that looks like this: A 1 2 B 1 2 Is there a SQL statement that will do this? I am using Oracle. Related questions: Returning multiple rows from a single row My question is close to the opposite of this question. Use LINQ to concatenate This is exactly what I want to do, but without LINQ

Aggregation in pandas

由 徘徊边缘 提交于 2019-11-26 00:43:59
问题 How to perform aggregation with pandas? No DataFrame after aggregation! What happened? How to aggregate mainly strings columns (to list s, tuple s, strings with separator )? How to aggregate counts? How to create new column filled by aggregated values? I\'ve seen these recurring questions asking about various faces of the pandas aggregate functionality. Most of the information regarding aggregation and its various use cases today is fragmented across dozens of badly worded, unsearchable posts

Inheritance vs. Aggregation [closed]

由 流过昼夜 提交于 2019-11-26 00:16:13
问题 There are two schools of thought on how to best extend, enhance, and reuse code in an object-oriented system: Inheritance: extend the functionality of a class by creating a subclass. Override superclass members in the subclasses to provide new functionality. Make methods abstract/virtual to force subclasses to \"fill-in-the-blanks\" when the superclass wants a particular interface but is agnostic about its implementation. Aggregation: create new functionality by taking other classes and

Prefer composition over inheritance?

由 六眼飞鱼酱① 提交于 2019-11-25 22:51:57
问题 Why prefer composition over inheritance? What trade-offs are there for each approach? When should you choose inheritance over composition? 回答1: Prefer composition over inheritance as it is more malleable / easy to modify later, but do not use a compose-always approach. With composition, it's easy to change behavior on the fly with Dependency Injection / Setters. Inheritance is more rigid as most languages do not allow you to derive from more than one type. So the goose is more or less cooked

What is the difference between association, aggregation and composition?

由 天大地大妈咪最大 提交于 2019-11-25 22:34:48
问题 What is the difference between association, aggregation, and composition? Please explain in terms of implementation. 回答1: For two objects, Foo and Bar the relationships can be defined Association - I have a relationship with an object. Foo uses Bar public class Foo { void Baz(Bar bar) { } }; Composition - I own an object and I am responsible for its lifetime. When Foo dies, so does Bar public class Foo { private Bar bar = new Bar(); } Aggregation - I have an object which I've borrowed from
订阅 aggregation