Select 列值大于另一列值的行

Question

我正在尝试获取比我的数据库中的特定作者拥有更多图书的所有作者的姓名。

架构：（LIVRO 表示 BOOK）

我有这个查询：

SELECT AUTORIA.CODAUTOR, AU.NOMEAUT, COUNT(AUTORIA.CODLIVRO) FROM AUTORIA
INNER JOIN AUTOR AS AU ON AU.CODIGO = AUTORIA.CODAUTOR
GROUP BY AUTORIA.CODAUTOR;

这就是 returns:

+----------+------------------+-------------------------+
| CODAUTOR | NOMEAUT          | COUNT(AUTORIA.CODLIVRO) |
+----------+------------------+-------------------------+
|        1 | MACHADO DE ASSIS |                       7 |
|        2 | NAVATHE          |                       6 |
|        3 | ELMASRI          |                       7 |
+----------+------------------+-------------------------+

现在我需要使用列 COUNT(AUTORIA.CODLIVRO) 的行过滤此结果，该列的值大于作者 NAVATHE 的此列的值。

那是我试过的：

SELECT AUTORIA.CODAUTOR, AU.NOMEAUT, COUNT(AUTORIA.CODLIVRO) FROM AUTORIA
INNER JOIN AUTOR AS AU ON AU.CODIGO = AUTORIA.CODAUTOR
GROUP BY AUTORIA.CODAUTOR /* Group books by author code */
/* Get authors with more books than NAVATHE */
HAVING COUNT(AUTORIA.CODLIVRO) > COUNT( /* Count how many books NAVATHE has */
    SELECT AUTORIA.CODLIVRO FROM AUTORIA /* Obtain the codes of the books of NAVATHE */
    INNER JOIN AUTOR AS AU ON AU.CODIGO = AUTORIA.CODAUTOR AND AU.NOMEAUT = 'NAVATHE'
);

但是这个查询给了我一个错误。

Answer 1

您可以简单地删除子查询周围的 COUNT()，并将其移动到子查询本身内：

SELECT AUTORIA.CODAUTOR, AU.NOMEAUT, COUNT(AUTORIA.CODLIVRO) FROM AUTORIA
INNER JOIN AUTOR AS AU ON AU.CODIGO = AUTORIA.CODAUTOR
GROUP BY AUTORIA.CODAUTOR
/* Get authors with more books than NAVATHE */
HAVING COUNT(AUTORIA.CODLIVRO) > (
    SELECT COUNT(AUTORIA.CODLIVRO) FROM AUTORIA /* Obtain the codes of the books of NAVATHE */
    INNER JOIN AUTOR AS AU ON AU.CODIGO = AUTORIA.CODAUTOR AND AU.NOMEAUT = 'NAVATHE'
);

Answer 2

嗯，获取 ID 的一种方法是：

SELECT a.CODAUTOR
FROM AUTORIA a
GROUP BY a.CODAUTOR
HAVING COUNT(*) > (SELECT COUNT(*)
                   FROM AUTORIA a2 JOIN
                        AUTOR au
                        ON au.CODIGO = a2.CODAUTOR
                   WHERE au.nome = 'NAVATHE'
                  );

我会让你计算 JOIN（或 IN 或 EXISTS 子句）来获取作者姓名。

Select 列值大于另一列值的行

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