java - 在 MySql 中合并两个 select 语句？

Question

我有这张 table ，看看那里。

create table if not exists thread_question
   (
    question_id INT NOT NULL auto_increment,
    first_name VARCHAR(100) NOT NULL,
    last_name VARCHAR(100) NOT NULL,
    question_title VARCHAR(500) NOT NULL,
    question VARCHAR(100000) NOT NULL,
    question_dateTime VARCHAR(100) NOT NULL,
    PRIMARY KEY(question_id)
  );

create table if not exists thread_answer
 (
  answer_id INT NOT NULL auto_increment,
  question_id INT NOT NULL references thread_question(question_id),
  first_name VARCHAR(100) NOT NULL,
  last_name VARCHAR(100) NOT NULL,
  answer VARCHAR(100000) NOT NULL,
  answer_dateTime VARCHAR(100) NOT NULL,
  PRIMARY KEY(answer_id)
 );

实际上我正在创建一个论坛来显示答案，它运行良好。您还可以看到 question_id 的列也插入到 thread_question 以及 thread_answer 中。我想在一个页面上显示我的答案，有多少用户在那里发布了答案。

所以我可以根据这个问题来做 -> How to show the numbers of answers posted into my forum?

问题

现在我试图将这两个语句结合起来:

第一句话:

SELECT thread_question.question_id, COALESCE(sub.counts,0) AS NumerOfAnswer 
   FROM thread_question LEFT JOIN (
        SELECT question_id, COUNT(answer_id) AS counts
        FROM thread_answer
        GROUP BY question_id
    ) sub ON thread_question.question_id = sub.question_id ORDER BY NumerOfAnswer asc

第二个声明:

select * from thread_question

实际上，我想从thread_question 的表 中获取用户的名字和名字、问题 和问题的标题。

我确实使用了 UNION 和 UNION ALL 和 SELECT( SELECT..)(SELECT..)。
但我无法显示结果.每次都给我一个错误。

请帮忙!!
当然，我们将不胜感激!!

Answer 1

由于您在查询中已经有了 thread_question 表，所以您需要做的就是添加 thread_question.*，就像这样:

SELECT
    thread_question.* -- <<== Use .* to bring all fields
,   COALESCE(sub.counts,0) AS NumerOfAnswer 
FROM thread_question
LEFT JOIN (
    SELECT question_id, COUNT(answer_id) AS counts
    FROM thread_answer
    GROUP BY question_id
) sub ON thread_question.question_id = sub.question_id
ORDER BY NumerOfAnswer asc