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添加新的MySQL表列并创建索引？

2024-05-18 05:15:04 421

要添加新的MySQL表列和索引，可以使用ALTERTABLE命令。

语法如下

ALTER TABLE yourTableName ADD COLUMN yourColumnName dataType,
ADD INDEX(yourColumnName );

为了理解上述语法，让我们创建一个表。创建表的查询如下

create table AddColumnAndIndexDemo
   -> (
   -> Id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
   -> Name varchar(100),
   -> Address varchar(200)
   -> );

现在，您可以检查表的描述。查询如下-

desc AddColumnAndIndexDemo;

以下是输出

+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| Id      | int(11)      | NO   | PRI | NULL    | auto_increment |
| Name    | varchar(100) | YES  |     | NULL    |                |
| Address | varchar(200) | YES  |     | NULL    |                |
+---------+--------------+------+-----+---------+----------------+
3 rows in set (0.03 sec)

以下是查询以添加新的MySQL表列和索引

alter table AddColumnAndIndexDemo add column Age int, add index(Age);
Records: 0 Duplicates: 0 Warnings: 0

再次检查表说明。查询如下-

desc AddColumnAndIndexDemo;

以下是输出

+---------+--------------+------+-----+---------+----------------+
| Field   | Type         | Null | Key | Default | Extra          |
+---------+--------------+------+-----+---------+----------------+
| Id      | int(11)      | NO   | PRI | NULL    | auto_increment |
| Name    | varchar(100) | YES  |     | NULL    |                |
| Address | varchar(200) | YES  |     | NULL    |                |
| Age     | int(11)      | YES  | MUL | NULL    |                |
+---------+--------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

使用SHOW命令从表中检查索引。查询如下-

show index from AddColumnAndIndexDemo;

以下是输出

+-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
| Table                 | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment | Visible |
+-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
| addcolumnandindexdemo | 0          | PRIMARY  | 1            | Id          | A         | 0           | NULL     | NULL   |      | BTREE      |         |               | YES     |
| addcolumnandindexdemo | 1          | Age      | 1            | Age         | A         | 0           | NULL     | NULL   | YES  | BTREE      |         |               | YES     |
+-----------------------+------------+----------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+---------+
2 rows in set (0.16 sec)

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添加新的MySQL表列并创建索引？

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