这个 UNION ALL mysql 查询有什么问题？

Question

SELECT 'Q' AS TYPE, 
       q.question AS value, 
       q.date
  FROM questions q
 WHERE q.user_id =39
UNION ALL 
SELECT 'A' AS TYPE, 
       q.question AS value, 
       a.date
  FROM answers a,
       questions q
 WHERE a.question_id = q.id
   AND WHERE a.user_id =39
ORDER BY `date` DESC

数据库设计：

• 问题{id，user_id，问题，日期}
• 答案{id，question_id，user_id，答案，日期}

错误：

1064 - 您的 SQL 语法有错误；检查与您的 MySQL 服务器版本相对应的手册，了解在 'WHERE a . user_id = 39 ORDER BY 日期 DESC

Answer 1

查询的下部有两个 WHERE 子句。您需要从字面上删除最后一个单词 WHERE。错误描述就是您所需要的。

Answer 2

“WHERE”出现两次。其中 x = ..... 且 ....

Answer 3

有一个额外的地方 a.user_id=39。您仅在子句开头使用关键字 WHERE (a.question_id = q.id AND a.user_id = 39)

SELECT 
'Q' AS TYPE , q.question AS value, q.date
FROM questions q
WHERE q.user_id =39
UNION ALL 
SELECT 'A' AS TYPE , q.question AS value, a.date
FROM answers a,questions q
WHERE a.question_id = q.id
AND
a.user_id =39
ORDER BY `date` DESC

Answer 4

正如错误试图解释的那样：对于第二个选择，您只需要输入一个“WHERE”。

SELECT 'A' AS TYPE , q.question AS value, a.date
FROM answers a,questions q
WHERE a.question_id = q.id
AND
a.user_id =39