MySQL跨表、多表更新SQL语句总结

单表更新

UPDATE table_name SET field1=new-value1, field2=new-value2 WHERE field=value

多表更新

情况一：

UPDATE userA as a , userB as b SET a.num = b.num*0.5 WHERE a.id = b.uid AND a.deleted_at is null;

UPDATE userA as a INNER JOIN userB as b ON a.id = b.uid SET a.num = b.num*0.5 WHERE AND a.deleted_at is null;

情况二：

UPDATE userA as a INNER JOIN userB as b ON a.id = b.uid SET a.num = b.num*0.5,a.state = 1 WHERE a.id = b.id 
AND a.deleted_at is null
AND (
	b.gb_name = 'a'
	OR b.gb_name = 'b'
	OR b.gb_name = 'c'
	OR b.gb_name = 'd'
	OR b.gb_name = 'e'
	OR b.gb_name = 'f'
	OR b.gb_name = 'g'
);

扩展：
inner join和where区别：
1 WHERE子句中使用的连接语句，在数据库语言中，被称为隐性连接。INNER JOIN……ON子句产生的连接称为显性连接。（其他JOIN参数也是显性连接）WHERE和INNER JOIN产生的连接关系，没有本质区别，结果也一样。但是！隐性连接随着数据库语言的规范和发展，已经逐渐被淘汰，比较新的数据库语言基本上已经抛弃了隐性连接，全部采用显性连接了。

2,测试结果inner join效率更快
事例：
Inner jion 原理：

SELECT
	*
FROM
	A
INNER JOIN B ON B.ID = A.ID
AND B.State = 1
INNER JOIN C ON B.ID = C.ID

where 原理：

SELECT
	*
FROM
	A
INNER JOIN B ON B.ID = A.ID
INNER JOIN C ON B.ID = C.ID
WHERE
	B.State = 1

INNER JOIN时会产生一个结果集，WHERE条件在这个结果集中再根据条件进行过滤。