sql子查询问题答案

【问题标题】：sql subquery problemsql子查询问题
【发布时间】：2010-12-19 16:38:32
【问题描述】：

我不会说英语。

我有一个 sql 子查询错误

数据库：MySQL
表类型：MyISAM

以下我的 sql 查询

SELECT
(SELECT sum(`total`) FROM `staff_history` WHERE `type` = 'Giriş' AND staff_id = table_1.staff_id) AS `input`,
(SELECT sum(`total`) FROM `staff_history` WHERE `type` = 'Çıkış' AND staff_id = table_1.staff_id) AS `output`,
(`input` - `output`) AS `balance`
FROM `staff_history` AS `table_1` WHERE `staff_id` = '2';

我收到这样的错误

Error code 1054, SQL status 42S22: Unknown column 'input' in 'field list'

你能帮我解决这个问题吗？

【问题讨论】：

您的英语足够好，可以在这里获得帮助。而且你的 SQL 也不错。
@dok 感谢您的好评

标签： mysql sql subquery mysql-error-1054

【解决方案1】：

您不能使用那里的字段名，因为它们在此范围内不可用。

你可以复制整个表达式

SELECT
(SELECT sum(`total`) FROM `staff_history` 
WHERE `type` = 'Giriş' AND staff_id = table_1.staff_id) AS `input`,
(SELECT sum(`total`) FROM `staff_history` 
WHERE `type` = 'Çıkış' AND staff_id = table_1.staff_id) AS `output`,
(SELECT sum(`total`) FROM `staff_history` 
WHERE `type` = 'Giriş' AND staff_id = table_1.staff_id) 
-
(SELECT sum(`total`) FROM `staff_history` 
WHERE `type` = 'Çıkış' AND staff_id = table_1.staff_id) AS `balance`
FROM `staff_history` AS `table_1` WHERE `staff_id` = '2';

查询优化器可以很好地处理这个问题，但它不是很容易维护，所以你也可以将整个查询放在一个子查询中：

SELECT
  x.`input`,
  x.`output`,
  x.`input` - x.`output` as `balance`
FROM
  (SELECT
    (SELECT sum(`total`) 
    FROM `staff_history` 
    WHERE `type` = 'Giriş' AND staff_id =  table_1.staff_id) AS `input`,
    (SELECT sum(`total`) 
    FROM `staff_history` 
    WHERE `type` = 'Çıkış' AND staff_id = table_1.staff_id) AS `output`
  FROM 
    `staff_history` AS `table_1` 
  WHERE `staff_id` = '2') x;

【讨论】：

【解决方案2】：

我提供 1 个 SQL 语句，1 个表扫描：

select sum(case when type = 'Giriş' then total else 0 end) as input
      ,sum(case when type = 'Çıkış' then total else 0 end) as output
      ,sum(case when type = 'Giriş' then total else 0 end) - 
       sum(case when type = 'Çıkış' then total else 0 end) as balance
  from staff_history
 where staff_id = 2
   and type in('Giriş', 'Çıkış');

【讨论】：