SQL通過參考表

Question

我在MySQL有三個表從另一個表插入方式：wp_usermeta，directory_department和directory_departmentmemebership

Directory_departmentmembership

| employee_id|department_id| 
|:-----------|------------:| 
| 1   |  2 |   
| 2   |  1 |  
| 3   |  3 |   

directory_department

| department_id|department_name| 
|:----------- |--------------:| 
| 1   |  Deans |   
| 2   |  MBA |  
| 3   |  Fiance | 

wp_usermeta有：

| employee_id| meta_key  | meta_value | 
|:-----------|--------------:|:------------:| 
| 1   |department_id |  2  | 
| 2   |department_id |  1  | 
| 3   |department_id |  3  | 
| 1   |department_name|    | 
| 2   |department_name|    | 
| 3   |department_name|    | 

我該如何引用directory_department，以便根據meta_value字段中的department_id值插入正確的department_name？

Answer 1

您可以使用SQL函數爲每個ID得到正確的名稱...

CREATE FUNCTION [dbo].[fn_department](@id INT) 
RETURNS VARCHAR(300) 
AS 
BEGIN 
    declare @department_name varchar(300) 
    select @department_name = department_name from directory_department where department_id = @id 

    RETURN @department_name 

END 

--And call it like this... 
INSERT INTO wp_usermeta (id,department_name) 
select id, dbo.fn_department(id) as department_name