Question

我的SQL语句看起来像那样

SELECT SQL_CALC_FOUND_ROWS q.id, q.question, sb.subject, c.chapter, sc.section, p.paragraph 
FROM questions AS q
     , subjects AS sb
     , sections AS sc
     , chapters AS c
     , paragraphs AS p 
WHERE (sb.id=q.subject AND c.id=q.chapter AND sc.id=q.section AND p.id=q.paragraph) AND (q.author_id=1) 
ORDER BY  q.id asc 
LIMIT 0, 25

如您所见，theese表格通过id相互关联。问题是，我正在subject列的questions列而不是subject表的subjects列。我在这里缺少什么？

请注意

我提供了主题作为例子。实际上，所有三个部分AS sc，章节AS c，段落AS p都不起作用。我只是受试者。

Answer 1

显然你的问题中的查询很好，但仍然要挖掘出来使用此语句，看看 subjects_subject 列中出现了什么：

SELECT SQL_CALC_FOUND_ROWS q.id, q.question, sb.subject as subjects_subject, c.chapter, sc.section, p.paragraph 
FROM questions AS q
     , subjects AS sb
     , sections AS sc
     , chapters AS c
     , paragraphs AS p 
WHERE (sb.id=q.subject AND c.id=q.chapter AND sc.id=q.section AND p.id=q.paragraph) AND (q.author_id=1) 
ORDER BY  q.id asc 
LIMIT 0, 25

希望这有帮助。

Answer 2

我通常显式使用JOIN语法。这有时会为您提供更好的错误输出，以帮助追踪问题。

这是原始格式，因此您可以轻松查看差异。

SELECT SQL_CALC_FOUND_ROWS q.id, q.question, sb.subject, c.chapter, sc.section, p.paragraph 
FROM questions AS q, 
     subjects AS sb, 
     sections AS sc, 
     chapters AS c, 
     paragraphs AS p 
WHERE (sb.id=q.subject 
       AND c.id=q.chapter 
       AND sc.id=q.section 
       AND p.id=q.paragraph) 
      AND (q.author_id=1) 
ORDER BY  q.id asc 
LIMIT 0, 25

这是编辑后的版本 - 请注意WHERE子句参数定义表挂钩在一起的方式是否已作为ON子句移动到表名列表中。这是INNER JOIN语法的一部分，它是：INNER JOIN ON。

SELECT SQL_CALC_FOUND_ROWS q.id, q.question, sb.subject, c.chapter, sc.section, p.paragraph 
FROM questions AS q
  INNER JOIN subjects AS sb ON sb.id = q.subject
  INNER JOIN sections AS sc ON sc.id = q.section 
  INNER JOIN chapters AS c ON c.id = q.chapter
  INNER JOIN paragraphs AS p ON p.id = q.paragraph
WHERE (q.author_id=1) 
ORDER BY  q.id asc 
LIMIT 0, 25

如果您尝试直接针对MySQL运行，会发生什么？

MySQL查询问题：无法从另一个表中选择列

2 个答案: