How to do it in MySql?

  

Use accumulators (or containers) in databases   It is never a good idea unless they can be "auditable". That is to say,   that it can be verified from some that the stored value is correct.

With this in mind, date the data structure that you pose, I would ask myself the following:

• Can I know who voted?
• Can I know how many points he gave him?
• Can I prevent the same user from voting infinitely on the same post?
• I want to be able to generate votes statistics?

Now, in response to the questions

  

Do I have to use two sql sentences? One to insert the points in the post field in the Bd and another one to insert it in the user's accumulated?

I suggest you make a detale table .

Seeing that you already have the tables users and posts , you should create a third table "posts_votes"

// TABLA posts_votos
|-------|----------|------|-----------|
|id_post|id_usuario|puntos|fecha      |
|-------|----------|------|-----------|
|1      |1         |10    |2016-10-26 |
|-------|----------|------|-----------|

This table allows:

• Register / Save : vote of a user on a post.

  $postId = 1;
  $idUsuario = 1;
  $puntos = 1;
  $query = 'INSER INTO posts_votos (id_post, id_usuario, puntos)
      VALUES ('.$postId.', '.$idUsuario.', '.$puntos.')';
  

• Control / Verify : if a user has already voted a post.

  $postId = 1;
  $idUsuario = 1;
  $query = 'SELECT * 
      FROM posts_votos
      WHERE id_post = '.$postId.' AND id_usuario = '.$idUsuario;
  

• Report / Consult :

  • How many votes and points a post has.

  $postId = 1;
  $query = 'SELECT SUM(puntos) AS puntosTotal,
        COUNT(puntos) AS votosTotal
      FROM posts_votos
      WHERE id_post = '.$postId;
  

  • How many votes and points a user made.

  $idUsuario = 1;
  $query = 'SELECT SUM(puntos) AS puntosTotal,
        COUNT(puntos) AS votosTotal
      FROM posts_votos
      WHERE id_usuario = '.$idUsuario;
  

  • How many votes and points the author of the post has.

  $idAutor = 1;
  $query = 'SELECT SUM(puntos) AS puntosTotal,
        COUNT(puntos) AS votosTotal
      FROM posts_votos
      WHERE id_posts IN (
        SELECT id_post 
        FROM posts
        WHERE id_autor = '.$idAutor.'
      )';
  

  • Also, if necessary, you can know how many votes a post / author received in the last month and / or how many votes a user gave.

  $idAutor = 1;
  $query = 'SELECT SUM(puntos) AS puntosTotal,
        COUNT(puntos) AS votosTotal
      FROM posts_votos
      WHERE fecha BETWEEN "2016-10-01" AND "2016-10-31"
      AND id_posts IN (
        SELECT id_post 
        FROM posts
        WHERE id_autor = '.$idAutor.'
      )';
  

  

but if I delete that post all the points will be deleted, and I do not want any of them to be erased, but those points remain accumulated

With this table, you will never lose that info.

I think you want to do it is the esquema of a base de datos with two tablas , something more or less like this:

// TABLA posts
|-------|----------|------|----|
|id_post|id_usuario|puntos|post|
|-------|----------|------|----|
|1      |1         |10    |POST|
|-------|----------|------|----|

// TABLA usuarios
|----------|-------|
|id_usuario|usuario|
|----------|-------|
|1         |LUIS   |
|----------|-------|

And to update the puntos in said post with respect to usuario (which is how I understand what you want) it would be with a simple query :

UPDATE posts SET puntos = 20 WHERE id_usuario = 1;

You can make a sum in the query, you do not have to store it in the separate database, I think it would go something like that

SELECT SUM(points) as puntos FROM post WHERE user_id = 1

you could also apply an average, something like user rating, that users rate the post with stars (1 to 5 stars) and you can take an average from the stars awarded to the post among the post that has had that user

What you ask for is done with the design you have put,

  

Do I have to use two sql statements?

You can make two queries or within the post table create a trigger that increases the Accumulated field

But as Marcos said well, in this way he is losing all kinds of traceability, from whom, when and how those points have arrived there.

Consider placing a field activo or visible in the table posts so that the posts do not erase them, you simply hide them from the user in this way:

• traceability of who has done everything
• if a post you really want that does not count for a vote because it does not meet certain requirements you can definitely delete it.
• "Deleted" posts keep adding up