如何使用 CASE 函数将 HIGHLIGHTED NULL 删除为 0答案

【问题标题】：How can I use CASE function to Remove HIGHLIGHTED NULL to 0如何使用 CASE 函数将 HIGHLIGHTED NULL 删除为 0
【发布时间】：2019-11-26 14:02:55
【问题描述】：

SELECT E.employee_id AS "EMPLOYEE ID", E.first_name AS "FIRST NAME", E.salary AS "SALARY",
       L.state_province AS "STATE", L.city AS "CITY",
       D.department_name AS "DEPARTMENT NAME"

FROM employees E Inner JOIN departments D
ON E.department_id = D.department_id
INNER JOIN locations L
ON D.location_id = L.location_id

【问题讨论】：

COALESCE( column, 'default value') 用于将 NULL 替换为默认值
我要使用 CASE FUNCTION
为什么要用'0' 替换州名？
我只是在练习，所以……不关注被替换的价值，而是关注如何替换它
请在问题中包含内容，而不是内容图片。

标签： mysql sql join inner-join

【解决方案1】：

只需替换：

L.state_province AS "STATE"

作者：

case when L.state_province is null then '0' else L.state_province end AS "STATE"

【讨论】：

不客气。请看What should I do when someone answers my question?

【解决方案2】：

如果你真的想要用例，那么你可以这样做：

SELECT 
     E.employee_id AS "EMPLOYEE ID", 
     E.first_name AS "FIRST NAME", 
     E.salary AS "SALARY",
     (CASE WHEN  L.state_province IS NULL THEN 0 ELSE  L.state_province END) AS "STATE", 
     L.city AS "CITY",
     D.department_name AS "DEPARTMENT NAME"
FROM employees E
Inner JOIN departments D ON E.department_id = D.department_id
INNER JOIN locations L ON D.location_id = L.location_id

【讨论】：

【解决方案3】：

在您的 SELECT 语句中，您可以使用 ISNULL() 函数包装您的列。

示例如下：-

SELECT E.employee_id AS "EMPLOYEE ID", E.first_name AS "FIRST NAME", E.salary AS "SALARY",
   ISNULL(L.state_province,'0') AS "STATE", L.city AS "CITY",
   D.department_name AS "DEPARTMENT NAME"

您也可以使用 CASE 语句，例如：

SELECT E.employee_id AS "EMPLOYEE ID", E.first_name AS "FIRST NAME", E.salary AS "SALARY",
   CASE WHEN L.state_province IS NULL then '0' ELSE L.state_province END AS "STATE", L.city AS "CITY",
   D.department_name AS "DEPARTMENT NAME"

【讨论】：