database-design

问题 This is my previous question: How can I merge two strings of comma-separated numbers in MySQL? I tried to use delimited list with these reasons: the data is more than 2000 rows. I have just one day. this is not production level I need to parse the data with my hands. I thought I don't have any choice. But I found this: SQL split values to multiple rows So, I got some hopes from it. But it's quite difficult to apply it to my table. Mine is different form. I have multiple columns and I'd like

问题 I am a beginner in NoSQL DB and Serverless. My app has a table called Trips . The parameters of the tables are {id, route, cost, selling, type, date, LR, asset } and a bunch of other irrelevant document numbers, where id is generated by uuid. Now I want to query the database for giving me Return all trips between a date range using the date parameter. Return all the trips for an asset in given period of time using date and asset parameter. Return all the trips for a route in a given period of

问题 Can a single column in a table can be referenced to multiple tables? 回答1: A very late answer, but for whoever is wondering & googeling. YES this can be done, but it is NOT good practice and even though it is quite simple, it will probably blow up in your face if you're not very aware of what you are doing. Not recommended. However, I can see uses. For instance, you have a large table of millions of records, and you want in exceptional cases link to unknown or multiple tables (in which case it

问题 When using Cloud Functions with the Firebase Realtime Database you are able to target a specific field with a cloud function. For example, given this JSON structure, I could target when user1's email field changed with a ('/user/{userId}/email').onUpdate cloud function. { "user": { "user1": { "name": "John Doe", "phone": "555-5555", "email": "john@gmail.com" } } } Now with Firestore it seems that I can't target a specific field and can only target documents. If this is the case a Firestore

问题 Background I am developing a social web app for poets and writers, allowing them to share their poetry, gather feedback, and communicate with other poets. I have very little formal training in database design, but I have been reading books, SO, and online DB design resources in an attempt to ensure performance and scalability without over-engineering. The database is MySQL, and the application is written in PHP. I'm not sure yet whether we will be using an ORM library or writing SQL queries

问题 We have a monolithic web based CRUD application (call it A ) which does a certain task. Now, we have a new requirement which is more or less independent of A functionally. The audience is different, the times of use, the functionality etc. are all different. Because of this, we decided to build this into a new service B . The problem started when B required authentication information from A . Anticipating that this might happen again, we pulled out the auth from A and put it as separate

问题 I have a question about database relationship I am trying to build a monitoring system with the following rules : Channels belongs to one Sensor Sensors belongs to one Device Devices belongs to one Probe Probes belongs to one Core Here is a preview of the tables +-------------+ +-------------+ | Cores | | Probes | +-------------+ +-------------+ | id | | id | | fields ... | | fields ... | +-------------+ | core_id | +-------------+ +-------------+ +-------------+ +-------------+ | Devices | |

问题 I have a question about database relationship I am trying to build a monitoring system with the following rules : Channels belongs to one Sensor Sensors belongs to one Device Devices belongs to one Probe Probes belongs to one Core Here is a preview of the tables +-------------+ +-------------+ | Cores | | Probes | +-------------+ +-------------+ | id | | id | | fields ... | | fields ... | +-------------+ | core_id | +-------------+ +-------------+ +-------------+ +-------------+ | Devices | |

问题 When your creating a database schema and come up with all the foreign keys. What are the advantages of explicitly defining them as such in the database? Are there advantages? If it's reliant MySQL is the db I will be using. 回答1: Foreign key constraints are used for maintaining Referential Integrity which is a database constraint that ensures that references between data are indeed valid and intact (a database should not only store data but should also ensure its quality). In other words, they

问题 Referring to the Postgres Documentation on Character Types, I am unclear on the point of specifying a length for character varying (varchar) types. Assumption: the length of string doesn't matter to the application. you don't care that someone puts that maximum size in the database you have unlimited hard disk space It does mention: The storage requirement for a short string (up to 126 bytes) is 1 byte plus the actual string, which includes the space padding in the case of character. Longer