获取特定列的SQL子查询

你不会说你在和哪个RDBMS合作。有些(如SQL Server)要求为内联视图提供表别名。很遗憾,我没有时间启动Windows VM进行复查,但您可以尝试:

SELECT username 
from (SELECT username, company, position 
    FROM table1 WHERE username IN 
        (SELECT username 
        FROM members_network 
        WHERE xscore <= 18 AND xscore >= 15)) T

需要为子查询分配表别名:

SELECT x.username 
  FROM (SELECT username, company, position 
          FROM table1 
         WHERE username IN (SELECT username 
                              FROM members_network 
                             WHERE xscore <= 18 AND xscore >= 15)) x

这个 x 是表别名。

根据注释,您似乎需要在子查询上添加别名。我还没有使用过这样的数据库,但我想有些数据库可以做到:

SELECT username from (SELECT username, company, position FROM table1 WHERE username IN (SELECT username FROM members_network WHERE xscore <= 18 AND xscore >= 15) AS USERNAMES) AS USERDETAILS

类似的东西应该可以工作(除非您的数据库有古怪的别名语法)。