relational-database

问题 I am developing an application using PHP and Yii Framework. I've been thinking about the most suitable database structure for the given functionality and here's what I've come up with. Yet I'm not 100% positive that's how it should be done so I've decided to ask the community. App Description: Registered users may participate in an event. Every event can have an unlimited number of users, called "participants of the event"). Once the event is over, every participant can leave a feedback about

问题 Consider the relation R(A, B, C, D, E, F, G) with the following types of attributes:- Total No of Keys = 1 = {A} Set of Simple (or) Atomic (or) Single Valued Attributes = {B, C} Set of Multivalued Attributes = {D, E} Set of Composite Attributes = { F, G} What would be the minimum no of tables that exists after decomposing relation R into 1NF? (A) 3 (B) 2 (C) 4 (D) 5 My attempt: We needed different table for each multivalued attributes with given key(A), total = 2 Similarly, we needed

问题 Sorry for that noob question but is there any real needs to use one-to-one relationship with tables in your database? You can implement all necessary fields inside one table. Even if data becomes very large you can enumerate column names that you need in SELECT statement instead of using SELECT * . When do you really need this separation? 回答1: 1 to 0..1 The "1 to 0..1" between super and sub-classes is used as a part of "all classes in separate tables" strategy for implementing inheritance. A

问题 I've been trying to see if I can accomplish some requirements with a document based database, in this case CouchDB. Two generic requirements: CRUD of entities with some fields which have unique index on it ecommerce web app like eBay (better description here). And I'm begining to think that a Document-based database isn't the best choice to address these requirements. Furthermore, I can't imagine a use for a Document based database (maybe my imagination is too limited). Can you explain to me

问题 I've been trying to see if I can accomplish some requirements with a document based database, in this case CouchDB. Two generic requirements: CRUD of entities with some fields which have unique index on it ecommerce web app like eBay (better description here). And I'm begining to think that a Document-based database isn't the best choice to address these requirements. Furthermore, I can't imagine a use for a Document based database (maybe my imagination is too limited). Can you explain to me

问题 I have the following tables in a relational database: [Sensor] LocationId [PK / FK -> Location] SensorNo [PK] [AnalogSensor] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] UpperLimit LowerLimit [SwitchSensor] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] OnTimeLimit [Reading] LocationId [PK/FK -> Sensor] SensorNo [PK/FK -> Sensor] ReadingDtm [PK] [ReadingSwitch] LocationId [PK/FK -> Reading] SensorNo [PK/FK -> Reading] ReadingDtm [PK/FK -> Reading] Switch [ReadingValue]

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 4 years ago . I'm starting a new project and would like to get my table- and column names right from the start. For example I've always used plural in table names but recently learned singular is correct. So, if I got a table "user" and then I got products that only the user will have,

问题 Recently NoSQL has gained immense popularity. What are the advantages of NoSQL over traditional RDBMS ? 回答1: Not all data is relational. For those situations, NoSQL can be helpful. With that said, NoSQL stands for "Not Only SQL". It's not intended to knock SQL or supplant it. SQL has several very big advantages: Strong mathematical basis. Declarative syntax. A well-known language in Structured Query Language (SQL). Those haven't gone away. It's a mistake to think about this as an either/or

问题 I'm doing some research into databases and I'm looking at some limitations of relational DBs. I'm getting that joins of large tables is very expensive, but I'm not completely sure why. What does the DBMS need to do to execute a join operation, where is the bottleneck? How can denormalization help to overcome this expense? How do other optimization techniques (indexing, for example) help? Personal experiences are welcome! If you're going to post links to resources, please avoid Wikipedia. I

问题 I am having some trouble getting the Yii2 RESTful API returning relational data. I have this working when viewed through the frontend but i am trying to get the same data through the API and its not working the same way. Tables country - PK is population_id population - Foreign Key is country.population_id I am getting this error: { "success": false, "data": { "name": "Invalid Configuration", "message": "The \"query\" property must be an instance of a class that implements the QueryInterface