For every row that moves, there are two actions - insert and delete.
对于所移动的每一行,有两个动作—insert和delete。
Notice the use of the index function within the at attribute of the insert and delete actions.
请注意insert和delete动作的at属性内index函数的使用。
In real life, you would rarely want to drop an existing database but merely INSERT and DELETE from tables.
在现实生活中,您不太会drop现有的数据库,而只是从表中INSERT和DELETE。
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