mysql modify content

MySQL is an open source relational database and one of the most popular databases today. Compared with other databases, MySQL has the advantages of simple use, high performance, stability and reliability. In actual applications, we may need to modify the content in MySQL to meet different needs. This article will introduce how to modify the content in MySQL.

1. Use the UPDATE statement to modify data rows

Modifying data rows in MySQL is a very common and important operation. We can use the UPDATE statement to modify one or more data rows. The basic syntax of the UPDATE statement is as follows:

UPDATE table_name SET col1=value1, col2=value2, ... WHERE condition;

Among them, table_name represents the table name to be modified; col1 and col2 represent the field names to be modified; value1 and value2 represent the field values ​​to be modified; WHERE condition represents the filtering condition.

For example, if we want to change the age in the record named Tom in the student table to 20, we can use the following UPDATE statement:

UPDATE student SET age=20 WHERE name='Tom';

This statement will change the name in the student table Change the age in Tom's record to 20.

2. Use the ALTER TABLE statement to modify the table structure

We can also use the ALTER TABLE statement to modify the table structure in MySQL, such as adding, deleting, and modifying fields in the table. The basic syntax of the ALTER TABLE statement is as follows:

ALTER TABLE table_name ADD column_name column_definition [FIRST|AFTER column_name];
ALTER TABLE table_name DROP column_name;
ALTER TABLE table_name MODIFY column_name column_definition;

Among them, the ADD clause means adding a field, the DROP clause means deleting a field, and the MODIFY clause means modifying the definition of a field. column_definition is the definition of the field, including field type, length, constraints, etc.

For example, we want to add a new field score in the student table. The field type is INT and the length is 3. We can use the following ALTER TABLE statement:

ALTER TABLE student ADD score INT(3);

This statement will be in Add a new field named score to the student table, with type INT and length 3.

You can also use the ALTER TABLE statement to modify the field definition. For example, if we want to change the score field type in the student table to FLOAT, with a length of 4, we can use the following ALTER TABLE statement:

ALTER TABLE student MODIFY score FLOAT(4);

This statement will change the score field type in the student table to FLOAT , length is 4.

3. Use the TRUNCATE TABLE statement to clear the table

The TRUNCATE TABLE statement can clear the data table in MySQL. The basic syntax of the TRUNCATE TABLE statement is as follows:

TRUNCATE TABLE table_name;

Among them, table_name represents the name of the table to be cleared.

For example, if we want to clear all data in the student table, we can use the following TRUNCATE TABLE statement:

TRUNCATE TABLE student;

This statement will clear all data in the student table.

4. Use the DROP TABLE statement to delete the table

The DROP TABLE statement can delete the table in MySQL. The basic syntax of the DROP TABLE statement is as follows:

DROP TABLE table_name;

Among them, table_name represents the name of the table to be deleted.

For example, if we want to delete the student table, we can use the following DROP TABLE statement:

DROP TABLE student;

This statement will delete the student table and all its data in MySQL.

5. Use the RENAME TABLE statement to rename the table

The RENAME TABLE statement can rename the table in MySQL. The basic syntax of the RENAME TABLE statement is as follows:

RENAME TABLE old_table_name TO new_table_name;

Among them, old_table_name represents the name of the table to be renamed, and new_table_name represents the new table name.

For example, if we want to rename the student table to stu, we can use the following RENAME TABLE statement:

RENAME TABLE student TO stu;

This statement will rename the student table in MySQL to the stu table.

In summary, we can use the UPDATE statement to modify the data rows in MySQL, use the ALTER TABLE statement to modify the table structure, use the TRUNCATE TABLE statement to clear the table, use the DROP TABLE statement to delete the table, use RENAME TABLE statement to rename the table. Using these statements, you can easily modify and manage the content in MySQL.

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