mysql - SELECT cols, (SELECT inner query) AS innercol FROM table WHERE innercol something

Question

只要我避免WHERE stream_json ...可以修复它还是需要加入，它就可以工作？

SELECT id, stuff,
    (SELECT count(*) 
     FROM inner_table
     WHERE inner_table.movie_id = outer_table.id) 
          AS stream_json
FROM outer_table 
WHERE stream_json != 0

Answer 1

您可以使用子句HAVING访问他们无法接受的自定义别名WHERE

SELECT (SELECT count(*) FROM inner_table
WHERE inner_table.movie_id = outer_table.id) AS stream_json
FROM outer_table HAVING stream_json != 0

请参阅此以供参考

Answer 2

您不能在 WHERE 条件中使用别名。但是，您可以在 HAVING 条件下使用它。另一种选择是重复整个子查询，但这看起来很难看。我建议使用 HAVING。

SELECT (SELECT count(*) FROM inner_table
WHERE inner_table.movie_id = outer_table.id) AS stream_json
FROM outer_table HAVING stream_json != 0

Answer 3

您无法访问同一级别的列别名。您需要将其包装到派生表中：

select *
from (
  SELECT id, 
         stuff,
         (SELECT count(*) 
          FROM inner_table
          WHERE inner_table.movie_id = outer_table.id) AS stream_json
  FROM outer_table
) t  
WHERE stream_json <> 0;

但 Kickstart 的答案可能是解决这个问题的更好方法。

Answer 4

如上所述，您可以使用 HAVING，或者您可以加入一个避免相关子查询的子选择

SELECT outer_table.id, outer_table.stuff, stream_json
FROM outer_table 
INNER JOIN
(
    SELECT movie_id, count(*) AS stream_json
    FROM inner_table
    GROUP BY movie_id
) Sub1
ON Sub1.movie_id = outer_table.id

请注意，您不需要检查 stream_json != 0 因为它隐含在 INNER JOIN 中