如何在mysql中的from子句中使用临时table？

Question

我正在尝试编写一个查询来获取 2019 年全年最高和第二低金额（工资 + 变量）的名称以及相应的金额值。

Employees Table:

| Emp_id | first_name | Last_name | Salary |   Joining_date    | Department|
|:------ |:----------:|:---------:|:------:|:-----------------:|:---------:|
|  001   | Manish     |  Agarwal  | 700000 |2019-04-20 09:00:00|    HR     |
|  002   | Niranjan   |  Bose     | 20000  |2019-02-11 09:00:00|    DA     |
|  003   | Vivek      |  Singh    | 100000 |2019-01-20 09:00:00|    DA     |
|  004   | Asutosh    |  Kapoor   | 700000 |2019-03-20 09:00:00|    HR     |
|  005   | Vihaan     |  Banerjee | 300000 |2019-06-11 09:00:00|    DA     |
|  006   | Atul       |  Diwedi   | 400000 |2019-05-11 09:00:00|  Account  |
|  007   | Sathyendra |  Tripathi | 95000  |2019-03-20 09:00:00|  Account  |
|  008   | Prithika   |  Bhatt    | 95000  |2019-03-20 09:00:00|    DA     | 


Variables table:

| Emp_Ref_ID | Variables_Date     | Variables_amount|
|:---------- |:------------------:|:---------------:|
|     1      |2019-02-20 00:00:00 |    15000        | 
|     2      |2019-06-11 00:00:00 |    30000        | 
|     3      |2019-02-20 00:00:00 |    42000        | 
|     4      |2019-02-20 00:00:00 |    14500        | 
|     5      |2019-06-11 00:00:00 |    23500        | 


Designation table:

| Emp_Ref_ID | Emp_title      |    Affected_from   |
|:---------- |:--------------:|:------------------:|
|     1      |  Asst.Manager  |2019-02-20 00:00:00 | 
|     2      | Senior Analyst |2019-01-11 00:00:00 | 
|     8      | Senior Analyst |2019-04-06 00:00:00 | 
|     5      |     Manager    |2019-10-06 00:00:00 | 
|     4      |  Asst.Manager  |2019-12-06 00:00:00 | 
|     7      |  Team Lead     |2019-06-06 00:00:00 | 
|     6      |  Team Lead     |2019-09-06 00:00:00 | 
|     3      | Senior Analyst |2019-09-06 00:00:00 |

我通过创建一个名为 t1 的 table 然后从中获取值来尝试下面的查询

select emp_title , emp_ref_id from 
(select d.emp_ref_id , d.emp_title, e.salary+v.variables_amount as full_amount from employees e join variables_details v on 
e.emp_id = v.emp_ref_id join designation d on v.emp_ref_id=d.emp_ref_id) as t1
where t1.emp_ref_id in (select t1.emp_ref_id from t1 where full_amount = (select max(full_amount) from t1) or full_amount = (select min(full_amount)
from t1 limit 1 offset 1);

但查询出错。

后来我决定创建一个临时的 table 然后从中获取数据。我使用了以下查询：

create temporary table temp (select d.emp_ref_id , d.emp_title, e.salary+v.variables_amount as full_amount from employees e join 
variables_details v on e.emp_id = v.emp_ref_id join designation d on v.emp_ref_id=d.emp_ref_id);

select emp_title, full_amount from temp where full_amount = (select max(full_amount) from temp) or
full_amount =  (select full_amount from temp order by full_amount asc limit 1 offset 1);

但它抛出了一个错误，指出“无法重新打开 table temp”。

这两种方法都不适合我。

我该如何处理这个问题？

Answer 1

正确的缩进有助于找到缺少的括号

在mysql8中可以使用With子句生成t1

查询#1

WITH t1 AS (select d.emp_ref_id , d.emp_title, e.salary+v.variables_amount as full_amount 
      from employees e join variables_details v on e.emp_id = v.emp_ref_id 
      join designation d on v.emp_ref_id=d.emp_ref_id)
select emp_title , emp_ref_id 
from 
    t1
where t1.emp_ref_id in (select 
                             t1.emp_ref_id 
                             from t1 
                             where full_amount = (select max(full_amount) from t1) 
                                                  or full_amount = (select min(full_amount)
                                                                    from t1 limit 1 offset 1)
                        );

emp_title	emp_ref_id
Asst.Manager	1

View on DB Fiddle

有了临时表，这一切变得更加复杂

CREATE TEMPORAry table  t1 (select d.emp_ref_id , d.emp_title, e.salary+v.variables_amount as full_amount 
      from employees e join variables_details v on e.emp_id = v.emp_ref_id 
      join designation d on v.emp_ref_id=d.emp_ref_id);
      
CREATE TEMPORAry table  t2 SELECT * FROM t1;
CREATE TEMPORAry table  t3 SELECT * FROM t1;
CREATE TEMPORAry table  t4 SELECT * FROM t1;

select emp_title , emp_ref_id 
from 
  t1
where emp_ref_id in (select 
                             emp_ref_id 
                             from t2
                             where full_amount = (select max(full_amount) from  t3) 
                                                  or full_amount = (select min(full_amount)
                          from t4 limit 1 offset 1)
                      );

emp_title    | emp_ref_id
:----------- | ---------:
Asst.Manager |          1

drop TEMPORAry table  t1;
drop TEMPORAry table  t2;
drop TEMPORAry table  t3;
drop TEMPORAry table  t4;

db<>fiddle here

如何在mysql中的from子句中使用临时table？

How to use temporary table in the from clause in mysql?

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