如何使用结构差异较大的Table B更新Table A中的Age字段？

要实现用Table B的Age字段值覆盖Table A中对应记录的Age字段（其余字段保留不变），核心是通过Name、Class、Subject、Marks这四个字段匹配两张表的对应记录（注：原描述中提到主键包含Age，但因Age是待更新字段，无法作为匹配条件，实际需用前四个字段关联）。以下是主流数据库的实现SQL：

MySQL #

使用UPDATE JOIN语法直接关联更新：

UPDATE TableA a
JOIN TableB b 
  ON a.Name = b.Name 
  AND a.Class = b.Class 
  AND a.Subject = b.Subject 
  AND a.Marks = b.Marks
SET a.Age = b.Age;

SQL Server #

通过UPDATE FROM实现关联更新：

UPDATE a
SET a.Age = b.Age
FROM TableA a
INNER JOIN TableB b 
  ON a.Name = b.Name 
  AND a.Class = b.Class 
  AND a.Subject = b.Subject 
  AND a.Marks = b.Marks;

Oracle #

提供两种写法，优先推荐MERGE语句：

方式1：MERGE语句 #

MERGE INTO TableA a
USING TableB b
ON (
  a.Name = b.Name 
  AND a.Class = b.Class 
  AND a.Subject = b.Subject 
  AND a.Marks = b.Marks
)
WHEN MATCHED THEN
  UPDATE SET a.Age = b.Age;

方式2：UPDATE子查询 #

UPDATE TableA a
SET a.Age = (
  SELECT b.Age 
  FROM TableB b 
  WHERE a.Name = b.Name 
    AND a.Class = b.Class 
    AND a.Subject = b.Subject 
    AND a.Marks = b.Marks
)
WHERE EXISTS (
  SELECT 1 
  FROM TableB b 
  WHERE a.Name = b.Name 
    AND a.Class = b.Class 
    AND a.Subject = b.Subject 
    AND a.Marks = b.Marks
);

执行以上SQL后，Table A的Age字段会与Table B对应记录的Age保持一致，Address、City等其他字段不受影响。

内容的提问来源于stack exchange，提问作者user22094638