Subquery with variable in where

I don't know why but if I do the subquery where in the first LEFT JOIN with the value of the variable @id it does not return any results, it is as if the value of @id was always null. **But why not do the LEFT JOIN directly?** Simple, the table is large and the query is taking horrors to execute, so it would be much faster. SELECT DISTINCT @id := p.id_pen, p.id_env_pen, 0 AS id_star, FALSE AS is_star, u.id_user AS sender_id, u.name_user AS sender_name, u2.id_user AS response_id, u2.name_user AS response_name, p.text_pen AS text_send, p2.text_pen AS text_response, DATE_FORMAT(p.created_at_pen, '%Y-%m-%d %H:%i:%s') AS send_datetime, DATE_FORMAT(p2.created_at_pen, '%Y-%m-%d %H:%i:%s') AS response_datetime, p.time_res_pen, p.state_pen, p.created_at_pen FROM pendency AS p LEFT JOIN ( SELECT p2.id_pen, p2.text_pen, p2.created_at_pen, p2.id_pen_req_pen FROM pendency AS p2 WHERE p2.id_pen_req_pen = @id # HERE, I try do = p.id_pen but dont works too, # id not identify the alias from outside ) AS p2 ON p2.id_pen_req_pen = @id INNER JOIN users AS u ON u.id_user = p.id_user_pen LEFT JOIN users AS u2 ON u2.id_user = p.id_user_req_pen WHERE (p.id_user_pen = '5' AND p.id_user_req_pen != -10) OR p.id_user_req_pen = '5' CREATE TABLES CREATE TABLE IF NOT EXISTS users ( id_user INT NOT NULL AUTO_INCREMENT PRIMARY KEY, id_fs_user VARCHAR(30) DEFAULT 'Não informado', email_user VARCHAR(105) DEFAULT 'Não informado', pass_user VARCHAR(35) DEFAULT 'Não informado', name_user VARCHAR(120) DEFAULT 'Não informado', cpf_user VARCHAR(15) DEFAULT 'Não informado', type_user VARCHAR(15) DEFAULT 'master', work_week_user INT DEFAULT 5, is_block_user BOOLEAN DEFAULT FALSE, permission_id_user INT NOT NULL DEFAULT 0, attendant_user BOOLEAN DEFAULT FALSE, version_id_user INT NOT NULL DEFAULT 0, last_login_user DATETIME, last_move_user DATETIME, id_user_user INT DEFAULT 0, created_at_user DATETIME DEFAULT CURRENT_TIMESTAMP, safe_del_date_user DATETIME DEFAULT CURRENT_TIMESTAMP, safe_del_state_user BOOLEAN DEFAULT FALSE, safe_del_user_user INT DEFAULT 0); CREATE TABLE IF NOT EXISTS pendency ( id_pen INT NOT NULL PRIMARY KEY AUTO_INCREMENT, id_env_pen INT NOT NULL, text_pen TEXT, id_user_req_pen INT DEFAULT 0, id_pen_req_pen INT DEFAULT 0, time_res_pen INT NOT NULL, state_pen BOOLEAN DEFAULT FALSE, id_old_pen INT NOT NULL, id_user_pen INT NOT NULL, created_at_pen DATETIME DEFAULT CURRENT_TIMESTAMP, FOREIGN KEY (id_env_pen) REFERENCES env(id_env) ON DELETE CASCADE);