mysql - SQL 通过引用表从另一个表插入

Question

我在 MySQL 中有三个表：wp_usermeta、directory_department 和 directory_departmentmemebership

Directory_departmentmembership

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

目录_部门

| 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|              |

我如何引用 directory_department 以根据 meta_value 字段中的 department_id 值插入正确的部门名称？

Answer 1

您可以使用 SQL 函数来获取每个 id 的正确名称...

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