mysql 俩个数据库，根据表下某列对应值替换其他列对应值

Question

2个数据库都是一样，一个新数据，一个旧数据
根据新数据某表下某列的值和旧数据某列对应的值（某列值一样，只是顺序不同），修改其他列对应的值

a数据库，b数据库都有表1，表1下都有z,x,y列
根据a数据库下表1，z列的对应值，替换到b数据库表1下的x,y列的对应值

Answer 1

按题主的假设两个数据库a和b,分别有表都为table1(含有x y z字段)
代码如下：

方法1：

UPDATE 
    a.table1 as t1, 
    b.table1 as t2 
SET 
    t2.x = t1.x, 
    t2.y = t1.y 
WHERE
    t2.z = t1.z;

方法2：

UPDATE 
    b.table1 as t2, 
LEFT JOIN
    a.table1 as t1 
ON
    t1.z = t2.z
SET 
    t2.x = t1.x, 
    t2.y = t1.y 

方法3：

UPDATE  
    b.table1 as t2
SET 
    t2.x = (SELECT t1.x from a.table1 as t1 where t2.z = t1.z limit 0,1), 
    t2.y = (SELECT t1.y from a.table1 as t1 where t2.z = t1.z limit 0,1) 
WHERE
    t2.z = t1.z;

Answer 2

update b set y = (select y from a where a.x = b.x limit 1 );