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    |         

directory_department

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

wp_usermeta：

| 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|              |

如何引用directory_department以根据meta_value字段中的department_id值插入正确的department_name？

Answer 1

您可以使用SQL函数为每个id获取正确的名称......

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