存储过程mysql中的多选语句
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【中文标题】存储过程mysql中的多选语句【英文标题】：multi select statement inside a stored procedure mysql 【发布时间】：2013-07-29 05:03:51 【问题描述】：我的 dbpre_exer5 中有这些表；//mysql wampserver2.2
+-----------------------+
| Tables_in_dbpre_exer5 |
+-----------------------+
| tblcourse |
| tblcutoff |
| tblgrades |
| tblstud |
| tblsub |
+-----------------------+
现在，我只想问一下，考虑到存储过程的使用情况，我将如何获得这些输出。 输出是：
+---------+----------------+---------------+-------+
| Gender | With Failure | W/out Failure | Total |
+---------+----------------+---------------+-------+
| Male | 1 | 1 | 2 |
| Female | 2 | 1 | 3 |
+---------+----------------+---------------+-------+
顺便说一下这里是enter code here;
**
mysql> select * from tblcourse;
+-----------+------------------------+
| course_id | course_name |
+-----------+------------------------+
| 1 | Information Technology |
| 2 | Computer Science |
+-----------+------------------------+
2 rows in set (0.00 sec)
mysql> select * from tblgrades;
+---------+--------+-------+
| stud_id | sub_id | grade |
+---------+--------+-------+
| 1 | 1 | 80 |
| 1 | 2 | 78 |
| 2 | 2 | 75 |
| 2 | 3 | 84 |
| 3 | 1 | 81 |
| 3 | 3 | 90 |
| 4 | 1 | 74 |
| 4 | 2 | 77 |
| 5 | 2 | 76 |
| 5 | 3 | 81 |
+---------+--------+-------+
10 rows in set (0.00 sec)
mysql> select * from tblcourse;
+-----------+------------------------+
| course_id | course_name |
+-----------+------------------------+
| 1 | Information Technology |
| 2 | Computer Science |
+-----------+------------------------+
2 rows in set (0.00 sec)
mysql> select * from tblcutoff;
+-----------+
| passgrade |
+-----------+
| 78 |
+-----------+
1 row in set (0.00 sec)
mysql> select * from tblgrades;
+---------+--------+-------+
| stud_id | sub_id | grade |
+---------+--------+-------+
| 1 | 1 | 80 |
| 1 | 2 | 78 |
| 2 | 2 | 75 |
| 2 | 3 | 84 |
| 3 | 1 | 81 |
| 3 | 3 | 90 |
| 4 | 1 | 74 |
| 4 | 2 | 77 |
| 5 | 2 | 76 |
| 5 | 3 | 81 |
+---------+--------+-------+
10 rows in set (0.00 sec)
mysql> select * from tblstud;
+---------+-------------------+--------+-----------+
| stud_id | stud_name | gender | course_id |
+---------+-------------------+--------+-----------+
| 1 | Angelina Jolie | F | 1 |
| 2 | Jennifer Garner | F | 1 |
| 3 | Liam Neeson | M | 2 |
| 4 | Paul Walker | M | 2 |
| 5 | Jennifer Lawrence | F | 2 |
+---------+-------------------+--------+-----------+
5 rows in set (0.00 sec)
mysql> select * from tblsub;
+--------+------------+
| sub_id | sub_name |
+--------+------------+
| 1 | Math 1 |
| 2 | English 1 |
| 3 | Filipino 1 |
+--------+------------+
3 rows in set (0.00 sec)
mysql>
**
我的第一个问题是在性别下得到“男性”和“女性”的结果。 有什么帮助吗？非常感谢。
【问题讨论】：
@Luv 我无法在存储过程中创建一个函数..我只是通过 select 语句做到了，但输出仍然是错误的 有没有办法从 3 个或多个表中获取值？ 复制：***.com/questions/4706100/… 【参考方案1】：更新
SELECT gender,
SUM(failure) `With failure`,
COUNT(*) - SUM(failure) `Without failure`,
COUNT(*) total
FROM
(
SELECT s.stud_id,
CASE WHEN s.gender = 'M' THEN 'Male' ELSE 'Female' END gender,
MAX(CASE WHEN g.grade < c.passgrade THEN 1 ELSE 0 END) failure
FROM tblgrades g JOIN tblstud s
ON g.stud_id = s.stud_id CROSS JOIN tblcutoff c
GROUP BY s.stud_id
) q
GROUP BY gender
示例输出：
|性别 |失败 |没有失败|总计 | -------------------------------------------------- - |女 | 2 | 1 | 3 | |男 | 1 | 1 | 2 |这里是SQLFiddle演示
【讨论】：
是的先生..但是失败的计数应该是唯一的..student_id 采用subj_id ..这意味着失败计数也必须与主题..stud_id&&subj_id 结合起来 @user2628953 它已经以这种方式“集成”在tblgrades 表中，不是吗？如果不是，请详细说明您的示例数据，什么应该和什么不应该被视为失败，我们可以修复查询。
say stud_id 4 has failed sub_id 1 和 2，查询应该只将此失败计为 1 .. 计数不取决于 stud_id 失败的主题数量，而是取决于 stud_id 是否有失败然后计数【参考方案2】：
你可以使用一个简单的case语句：
CASE WHEN 'F' THEN SELECT 'Female' ELSE SELECT 'Male'
Further reading
【讨论】：
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