Question

我在设置查询时遇到问题

(SELECT * FROM attendance WHERE am_slip="absent" AND pm_slip="none")
 UNION
(SELECT * FROM attendance WHERE am_slip="none" AND pm_slip="absent")
 UNION
(SELECT * FROM attendance WHERE am_slip="absent" AND pm_slip IS NULL)
 UNION
(SELECT * FROM attendance WHERE am_slip="absent" AND pm_slip="late")
 UNION
(SELECT * FROM attendance WHERE am_slip="late" AND pm_slip="absent")
 UNION
(SELECT * FROM attendance WHERE am_slip="absent" AND pm_slip="absent")

我想合并/合并数据表（ID号）中的所有事件，但我做不到。那么，你能帮我吗？

这是使用上面的查询的输出：

这是我想要的输出：

至

这是表格，我想合并它们并显示单个输出：

实验查询但不起作用：

选择stu_id，从中选择COUNT（*）AS id_count（选择*从出勤地点am_slip =“ late”和pm_slip =“ none”）联盟（选择*从出勤地点，其中am_slip =“ none”和pm_slip =“ late”）联盟（选择*从出勤地点，其中am_slip =“ late”和pm_slip为NULL）联盟（选择*从出勤地点，其中am_slip =“ late”和pm_slip =“ absent”）联盟（选择*从出勤地点，其中am_slip =“ absent”和pm_slip =“ late”）联盟（选择*从出勤地点，其中am_slip =“ late”和pm_slip =“ late”） GROUP BY stu_id ORDER BY id_count

Answer 1

如果要获得独特的结果，则可以正确使用UNION，但在这种情况下，应避免选择*（选择所有列），应明确选择涉及的列

SELECT name, ID_No, Num_Absence, Handle 
FROM attendance WHERE am_slip="absent" AND pm_slip="none")
  UNION
SELECT name, ID_No, Num_Absence, Handle 
FROM attendance WHERE am_slip="none" AND pm_slip="absent"
  UNION
SELECT name, ID_No, Num_Absence, Handle 
FROM attendance WHERE am_slip="absent" AND pm_slip IS NULL
  UNION
SELECT name, ID_No, Num_Absence, Handle 
FROM attendance WHERE am_slip="absent" AND pm_slip="late"
  UNION
SELECT name, ID_No, Num_Absence, Handle 
FROM attendance WHERE am_slip="late" AND pm_slip="absent"
  UNION
SELECT name, ID_No, Num_Absence, Handle 
FROM attendance WHERE am_slip="absent" AND pm_slip="absent"

Answer 2

下面将通过DISTINCT给出示例，并使用WHERE子句上的ORs操作数替换所有UNION子句：

SELECT
    DISTINCT name, ID_No, Num_Absence, Handle 
FROM
    attendance
WHERE
    (am_slip="absent" AND (pm_slip="none" OR pm_slip IS NULL OR pm_slip="late" OR pm_slip="absent"))
OR
    (am_slip="none" AND pm_slip="absent")
OR
    (am_slip="late" AND pm_slip="absent")

Answer 3

完成谢谢你们对我的帮助

选择idnum.stu_id，从（选择*来自出席者的COUNT（*）中，am_slip =“ absent”和pm_slip =“ none” 全联盟选择*从出勤地点，其中am_slip =“ none”和pm_slip =“ absent” 全联盟 SELECT * FROM出勤，其中am_slip =“ absent”和pm_slip为NULL 全联盟选择*从出勤地点，在am_slip =“ absent”和pm_slip =“ late” 全联盟选择*从出勤地点，在am_slip =“ late”和pm_slip =“ absent” 全联盟选择*从出席者中，将am_slip =“ absent”和pm_slip =“ absent”）作为idnum GROUP BY stu_id 排序stu_id

联合选择和组出现

3 个答案: