如何在mysql中复制表行？

Question

这是我的表farm：

+--------+
| animal |
+--------+
| cat    |
| monkey |
| bird   |
| dog    |
| horse  |
+--------+

我想要对行animal进行精确复制。所以我的表应该是这样的：

+--------+---------+
| animal | animal2 |
+--------+---------+
| cat    | cat     |
| monkey | monkey  |
| bird   | bird    |
| dog    | dog     |
| horse  | horse   |
+--------+---------+

我试过

INSERT INTO `farm` (`animal2`) SELECT `animal` FROM `animals`

但是会发生什么：

+--------+---------+
| animal | animal2 |
+--------+---------+
| cat    |         |
| monkey |         |
| bird   |         |
| dog    |         |
| horse  |         |
|        | cat     |
|        | monkey  |
|        | bird    |
|        | dog     |
|        | horse   |
+--------+---------+

Answer 1

为避免删除表中不相关的数据，请使用以下方法。

DELETE FROM `farm` WHERE `animal1` IN (SELECT `animal` FROM `animals`);
INSERT INTO `farm` (`animal`, `animal2`) SELECT `animal`, `animal` FROM `animals`;

Answer 2

首先，您应该添加新列（具有相同的数据类型）和NULL：

ALTER TABLE `farm` ADD `animal2` VARCHAR(100);

然后只需更新：

UPDATE `farm` SET `animal2` = `animal`;

如果您需要使用NOT NULL再次使用NOT NULL属性更改表。

的 LiveDemo

输出：

╔════════╦═════════╗
║ animal ║ animal2 ║
╠════════╬═════════╣
║ cat    ║ cat     ║
║ monkey ║ monkey  ║
║ bird   ║ bird    ║
║ dog    ║ dog     ║
║ horse  ║ horse   ║
╚════════╩═════════╝