將查詢結果更新至資料表 UPDATE for SELECT [MySQL]

今天又學到一個 MySQL 新方法，原本就在找利用 SELECT 的結果 UPDATE 至資料表的方法，最後終於在 MySQL 官網中的回應裡找到了

原始碼

1. UPDATE 
2.    `t1` AS A, 
3.    (SELECT `b1`, COUNT(*) AS `total` FROM `t2` GROUP BY `c1`) AS B 
4. SET A.`a2`=B.`total` 
5. WHERE A.`a1`=B.`a1` 

UPDATE
    `t1` AS A,
    (SELECT `b1`, COUNT(*) AS `total` FROM `t2` GROUP BY `c1`) AS B
SET A.`a2`=B.`total`
WHERE A.`a1`=B.`a1`

MySQL5.0: UPDATE Syntax