从3个表中创建一个选择

Question

I´m trying to create a select from 3 different tables. I want to show the name of the student, his class and the date of register. I have 3 tables "aluno" (student), "turma" (class) and "data..." (date). The name of the student is on the first table named "aluno". The class of the stundet is on the table named "turma". The register on the class is on the table named "matricula". My objetive is to show the name of the stundent, the name of the class (designacao) and the date (data). My function that does this sql command is doing a join, but i´m not sure if its ok.. I think the select is wrong.

function DBRead15()

$sql="SELECT aluno.nome as nome, matricula.*, turma.* 
  FROM matricula
  LEFT JOIN aluno ON aluno.n_processo = matricula.n_processo";
$result=DBExecute($sql);

while($res=mysqli_fetch_assoc($result))
{
    $data[]=$res;
}
return $data;

Answer 1

You started doing the query partially, but can continue as follows:

SELECT aluno.nome as nome, turma.designacao, matricula.data
FROM aluno
LEFT JOIN turma ON aluno.n_processo = matricula.n_processo
LEFT JOIN matricula ON turma.idturma = matricula.turma

This query assigns the connection between aluno and turma as aluno_id (one-to-many relationship) and the connection between turma and matricula as turma_id (one-to-many relationship). This query may not work perfectly for you, you will have to change aluno_id to whatever column connects your students to their classes.

This query is an example of how table JOIN in SQL.

Answer 2

Looking to your tables

  SELECT aluno.nome as nome, matricula.*, turma.* 
  FROM matricula
  LEFT JOIN aluno ON aluno.n_processo = matricula.n_processo
  LEFT JOIN turma ON matricula.turma = turma.idturma