语法错误或访问冲突：1066 不是唯一的表/别名：'tasks'

Question

I keep getting this error, and found only answers to users of laravel..

I have this query:

  $stmt = $pdo->query("SELECT branches.branch_id, branches.branch_name,
        tasks.task_name, tasks.task_status, tasks.real_amount,
        tasks.task_start, tasks.task_finish, tasks.description, projects.proj_name, projects.project_id
        FROM retail2.branches, retail2.projects, retail2.tasks
        JOIN tasks ON tasks.branch_id = branches.branch_id;
        JOIN branches_projects ON projects.project_id = branches_projects.proj_id
        JOIN branches ON branches.branch_id = branches_projects.branch_id");

and I've been trying to debug but I can't find out what the issue is... any suggestion please? Thanks!

Answer 1

You don't need to list tables in both the FROM and JOIN clauses. You just need to reorder the JOIN clauses, because a JOIN can only refer to tables in previous JOIN or FROM clauses.

You also have a ; in the middle of the query, at the end of the JOIN tasks line. Everything after that is not part of the query, and this will cause an error becauase PDO doesn't allow multiple queries in one call.

SELECT branches.branch_id, branches.branch_name,
    tasks.task_name, tasks.task_status, tasks.real_amount,
    tasks.task_start, tasks.task_finish, tasks.description, projects.proj_name, projects.project_id
    FROM projects
    JOIN branches_projects ON projects.project_id = branches_projects.proj_id
    JOIN branches ON branches.branch_id = branches_projects.branch_id
    JOIN tasks ON tasks.branch_id = branches.branch_id;