蓬勃发展：如何选择一对多

Question

Let's suppose there is a set of A and for each a of A there is a set of B. In short: A:B = 1:n

Let's suppose, there is an a, which is an A and it is interesting. However, I would like to select a with all its B elements.

For instance, let's consider the example of Companies and Workers. For the sake of simplicity, we assume that a Worker works at a single Company and a Company might have a natural number of Workers.

If I want to select a set, containing the values of Company.Name, Worker.Name of a given Company, then what should I do in PHP, to achieve the expected result?

Answer 1

Based on your example, assuming you have this schema

Table Company

• CompanyID (PK)
• CompanyName
• other columns..

Table Worker

• WorkerID (PK)
• WorkerName
• CompanyID (FK)

You can join the tables by linking Company and Worker with CompanyID

SELECT  a.Name CompanyName,
        b.Name WorkerName
FROM    Company a
        INNER JOIN Worker b
            ON a.CompanyID = b.CompanyID

To further gain more knowledge about joins, kindly visit the link below:

• Visual Representation of SQL Joins