mysql行命令重新计算

Question

假设我们有表：

announces_id    announces_pos   announces_title

如何通过单个查询重新计算所有announces_pos？ 例： 将announces_pos设置为id 2上的3，所有下一行（announces_pos＆gt; 3）应重新计算

Answer 1

你需要处于旧位置。比增加旧的和新的之间的所有位置。

DO @old_pos:=announces_pos FROM announces WHERE announces_id = 2;
UPDATE announces SET announces_pos = IF(announces_id = 2, 3, announces_pos + 1) WHERE announces_pos BETWEEN 3 AND @old_pos;