MySql添加索引：0行受影响 [英] MySql Add Index : 0 Rows Affected

问题描述

Alter table table1 add index col1_idx (column1);

即使table1有很多行，并且所有列都具有非空值，上面的查询说0行被发现。为什么会这样？

Even though the table1 has many rows and all of the have non null values for column1, the above query says "0 Rows AFfected". Why could this be?

推荐答案

这是因为查询不直接影响任何行，而不是您修改的更新语句这一排。它（非常，非常，非常基本）只改变列的存储和排序方式。

That is because the query is not directly affecting any rows as opposed to an update statement where you modify the row. It (very, very, very basically) only changes how the column is stored and sorted.

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