为每列更新具有不同条件的多列？

Question

在学生表中，我有 'null' 和 ('') 空单元格。有没有办法通过对每列使用不同的条件来更新多列？

我已经尝试了如下几个查询，但没有按计划进行

第一个：

update student_info SET email_id = Null, department = NULL, scholarship = NULL WHERE EXISTS (
SELECT email_id,department,scholarship from student_info WHERE 
(email_id in ('null','') or department in ('null', '') or scholarship in ('null', '')));
GO

第二个：

UPDATE student_info SET 
        email_id = CASE  WHEN ( email_id in ('null','')) THEN NULL END,
        department = CASE WHEN (department in ('null','')) THEN NULL END,
        scholarship = CASE WHEN (scholarship in ('null','')) THEN NULL END,
        location = CASE WHEN (location in ('null','')) THEN NULL END
        GO

我该如何解决这个问题？

表：

CREATE TABLE student_info ( student_id INT, email_id varchar(15), scholarship 
VARCHAR(5),location varchar(20), department VARCHAR(15), phone varchar(15));
GO

价值：

INSERT INTO student_info 
VALUES 
(1002,'1002@uni.com', 'Yes', 'null','', '+00000002'),
(1003,'null', 'Yes', 'International','', '+00000003'),
(1004,'1004@uni.com', 'null', '','English', '+00000004'),
(1005,'null', 'Yes', 'Domestic','', '+00000005'),
(1006,'null', 'Yes', 'Domestic','English', ''),
(1007,'', 'Yes', 'Domestic','English', '+00000007'),
(1009,'1001@uni.com', 'null', 'Domestic','English', '+00000009');
 GO

Answer 1

我认为这会更简单地写成：

UPDATE student_info 
    SET email_id = (CASE WHEN email_id NOT IN ('null', '') THEN email_id END),
        department = (CASE WHEN (department NOT IN ('null', '') THEN department END),
        scholarship = (CASE WHEN scholarship NOT ('null', '') THEN scholarship END),
        location = (CASE WHEN location NOT IN ('null', '') THEN location END)
WHERE email_id IN ('null', '') OR
      department IN ('null', '') OR
      scholarship IN ('null', '') OR
      location IN ('null', '');

变化是：

1. CASE 表达式现在在 no 匹配时返回列。缺少的ELSE 意味着匹配总是NULL。
2. WHERE 子句不使用子查询。这是完全没有必要的。
3. WHERE 子句检查所有四列。

在 SQL Server 中，最好使用WHERE 子句过滤掉不会发生更改的记录。即使记录没有更改，SQL Server 也会“进行更新”。

Answer 2

您的“case when”选项缺少“ELSE”和“WHERE”：

我添加了 2 并且它可以工作 (sqlfiddle to see the result)：

UPDATE student_info SET 
        email_id = (CASE  WHEN ( email_id in ('null','')) THEN NULL ELSE email_id END),
        department = (CASE WHEN (department in ('null','')) THEN NULL ELSE department END),
        scholarship = (CASE WHEN (scholarship in ('null','')) THEN NULL ELSE scholarship END),
        location = (CASE WHEN (location in ('null','')) THEN NULL ELSE location END)
WHERE EXISTS (
SELECT email_id,department,scholarship from student_info WHERE 
(email_id in ('null','') or department in ('null', '') or scholarship in ('null', '')));