Junior — Middle

Can you list the main types of relationships used in SQL relational databases?

sobes.tech AI

Answer from AI

In relational databases, the main types of relationships between tables are:

One to one (1:1) — each record in the first table corresponds to exactly one record in the second table and vice versa.
One to many (1:N) — one record in the first table corresponds to multiple records in the second.
Many to many (M:N) — records in one table can correspond to many records in another and vice versa. Usually, an intermediate linking table is used to implement this.

Example of a "one to many" relationship:

-- Users table
CREATE TABLE Users (
  UserID INT PRIMARY KEY,
  UserName VARCHAR(100)
);

-- Orders table
CREATE TABLE Orders (
  OrderID INT PRIMARY KEY,
  UserID INT,
  OrderDate DATE,
  FOREIGN KEY (UserID) REFERENCES Users(UserID)
);

Here, one user can have many orders.

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