junction-table

问题 I am creating a schema where the following logic applies: A String can belong to multiple locations. Multiple Locations can have multiple String , or no String . The DateTime (As DateScraped ) at which the relationship between Location and String was formed must be recorded. Basically, I've mapped the relationship as a many-to-many relationship using a junction table like so: In mapping the chart in Code First EF6 (Using SQLite), I have the following objects: public class Location { [Key,

问题 I am creating a schema where the following logic applies: A String can belong to multiple locations. Multiple Locations can have multiple String , or no String . The DateTime (As DateScraped ) at which the relationship between Location and String was formed must be recorded. Basically, I've mapped the relationship as a many-to-many relationship using a junction table like so: In mapping the chart in Code First EF6 (Using SQLite), I have the following objects: public class Location { [Key,

问题 I am creating a schema where the following logic applies: A String can belong to multiple locations. Multiple Locations can have multiple String , or no String . The DateTime (As DateScraped ) at which the relationship between Location and String was formed must be recorded. Basically, I've mapped the relationship as a many-to-many relationship using a junction table like so: In mapping the chart in Code First EF6 (Using SQLite), I have the following objects: public class Location { [Key,

问题 I am making a database for a freelance sign language interpreter. I have a subject table tblClient which holds information regarding the freelancer's clients. There is a lookup table tlkClient ClientType showing the various types of clients (categorized on condition -- deaf, deaf/blind, etc). There is also a table called tlkClient Modality. In this table are the different types of sign language offered by the interpreter. You can pick the client's preferred modality from the Client table. Now

来源： https://stackoverflow.com/questions/33952849/use-1-junction-table-with-3-foreign-keys-or-2-junction-tables-with-shared-sequen

问题 I'm making hashtag system for my webpage, and have three tables: items - ID and some others tags - ID and name item_tags - junction table with IDitem and IDtag Selecting all items with given hashtag is pretty easy: SELECT items.* FROM items join item_tags on items.ID=item_tags.IDitem join tags on item_tags.IDtag=tags.ID where tags.name="something"; Question is, what should I do if I want to select all items with multiple tags, for example, find all items tagged as cat and animal? I've thought

问题 I have items and units table that have many to many relationship. In other words, the item has many units and the unit has many items. I managed the relation through a junction table item_units . The junction table has some extra field more than item_id and unit_id , i.e it has price, and weight (it is an integer to manage the order of units for each item for display purposes). I managed the relations in the models as follows: //In Items model /** * @return \yii\db\ActiveQuery */ public

问题 I'm modeling many-to-many relationship where the relationship is accessed most of the time from one side only. It's more like a hierarchy, that is accessed top-down and not the other way around. Survey has and belongs to many Questions has and belongs to many Answers . Both relationships must be many-to-many because a same question can be re-used across different surveys and same answer in many questions. This is a requirement. The standard M2M implementation would use two junction tables,

问题 create_table :categories_posts, :id => false do |t| t.column :category_id, :integer, :null => false t.column :post_id, :integer, :null => false end I have a join table (as above) with columns that refer to a corresponding categories table and a posts table. I wanted to enforce a unique constraint on the composite key category_id, post_id in the categories_posts join table. But Rails does not support this (I believe). To avoid the potential for duplicate rows in my data having the same

问题 I have a table Messages with columns ID (primary key, autoincrement) and Content (text). I have a table Users with columns username (primary key, text) and Hash. A message is sent by one Sender (user) to many recipients (user) and a recipient (user) can have many messages. I created a table Messages_Recipients with two columns: MessageID (referring to the ID column of the Messages table and Recipient (referring to the username column in the Users table). This table represents the many to many