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A case where mysql changes the data type of a field in a table? This problem may be often seen in our daily study or work. I hope you can gain a lot from this question. The following is the reference content that the editor brings to you, let's take a look at it!

In mysql, you can use the "ALTER TABLE" statement with the "MODIFY" keyword to change the data type of a field in the table; the syntax format is "ALTER TABLE MODIFY".

In MySQL, the ALTER TABLE statement can change the structure of the original table, such as adding or deleting columns, changing the original column type, renaming the column or table, and so on.

The syntax format is as follows:

ALTER TABLE [modify options]

The syntax format of the modification option is as follows:

{ADD COLUMN

| | CHANGE COLUMN |

| | ALTER COLUMN {SET DEFAULT | DROP DEFAULT} |

| | MODIFY COLUMN |

| | DROP COLUMN |

| | RENAME TO |

| | CHARACTER SET |

| | COLLATE} |

Modify field data type

To change the data type of a field is to convert the data type of the field to another data type. The syntax rules for modifying field data types in MySQL are as follows:

ALTER TABLE MODIFY

Where:

Table name: refers to the name of the table where the field of the data type is to be modified

Field name: refers to the field to be modified

Data type: refers to the new data type of the modified field.

Example:

Create a new student data table in the test database, and the SQL statement and run result are as follows:

Mysql > USE test;Database changedmysql > CREATE TABLE student (- > id INT (4),-> name VARCHAR (20),-> sex CHAR (1); Query OK, 0 rows affected (0.09 sec)

Use DESC to view the student table structure, the SQL statement and the run result are as follows:

Mysql > DESC student +-+ | Field | Type | Null | Key | Default | Extra | +-+- -+ | id | int (4) | YES | | NULL | name | varchar (20) | YES | | NULL | | sex | char (1) | YES | | NULL | | +-+-+ 3 rows in set (0.01sec)

Use ALTER TABLE to modify the structure of the table student, changing the data type of the name field from VARCHAR (20) to VARCHAR (30). The SQL statement and run results are shown below.

Mysql > ALTER TABLE student-> MODIFY name VARCHAR (30); Query OK, 0 rows affected (0.15 sec) Records: 0 Duplicates: 0 Warnings: 0mysql > DESC student +-+-+ | Field | Type | Null | Key | Default | Extra | + -+ | id | int (11) | YES | | NULL | name | varchar (30) | YES | | NULL | | sex | char (1) | YES | | NULL | | +-+-+ 6 rows in set (0.00 sec)

After the statement is executed, it is found that the data type of the name field in the table student has been changed to VARCHAR (30), and the modification is successful.

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