MySQL UPDATE JOIN

MySQL UPDATE JOIN语法:

UPDATE T1, T2,
[INNER JOIN | LEFT JOIN] T1 ON T1.C1 = T2. C1
SET T1.C2 = T2.C2, 
    T2.C3 = expr
WHERE condition 

还有另一种使用以下语法更新数据交叉表的方法：

UPDATE T1, T2
SET T1.c2 = T2.c2,
      T2.c3 = expr
WHERE T1.c1 = T2.c1 AND condition 

等价于：

UPDATE T1,T2
INNER JOIN T2 ON T1.C1 = T2.C1
SET T1.C2 = T2.C2,
      T2.C3 = expr
WHERE condition 

例子：

UPDATE employees
        LEFT JOIN
    merits ON employees.performance = merits.performance 
SET 
    salary = salary + salary * 0.015
WHERE
    merits.percentage IS NULL;