Mysql 在同一查询中使用查询值

如果有一个查询有两个选择，我可以在第二个选择中使用第一个选择的值吗

i、 e:

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上面的方法不起作用，我该怎么做呢？

这取决于您试图做什么，您可以使用子查询来获取WHERE子句的结果

比如说

SELECT post_id AS post_2 FROM posts
WHERE user_id = (SELECT post_id AS post_1 FROM posts WHERE user_id = 100)

SET myVar = (SELECT post_id AS post_1 FROM posts WHERE user_id = 100);

SELECT post_id AS post_2 FROM posts WHERE user_id = myVar  

或者，您可以按顺序运行两个查询，将第一个结果分配给一个变量并使用该变量

比如说

SELECT post_id AS post_2 FROM posts
WHERE user_id = (SELECT post_id AS post_1 FROM posts WHERE user_id = 100)

SET myVar = (SELECT post_id AS post_1 FROM posts WHERE user_id = 100);

SELECT post_id AS post_2 FROM posts WHERE user_id = myVar  

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看起来你想加入

SELECT p1.post_id as post_id1
     , p2.post_id as post_id2
  FROM posts p1
  JOIN posts p2
    ON p2.user_id = p1.post_id
 WHERE p1.user_id = 100;

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这将只返回其中一个查询的结果。我需要能够返回两个查询的单独结果。好吧，我想我误解了您的意图，在这种情况下，您可能希望执行Hartmut建议的自连接。