mysql change data

MySQL is an open source relational database management system with the advantages of low cost, easy expansion, and high reliability. It is widely used in various enterprise fields. In the actual application process, the data in MySQL often needs to be modified and updated. This article will introduce how MySQL performs data changes.

1. Overview of SQL Language

SQL "Structured Query Language" is a structured query language, which is a standard language for adding, deleting, modifying, and querying, and managing data. SQL includes three parts: data definition, data operation and data control:

1. Data Definition Language (DDL): including creating, modifying and deleting databases, tables, columns, etc.

2. Data manipulation language (DML): including query, insert, update and delete operations.

3. Data Control Language (DCL): includes operations such as permission control.

2. How to change data

1. Update a single piece of data

When some fields in the data need to be changed, you can use the UPDATE keyword to update a single piece of data. The basic syntax is as follows:

UPDATE 表名 SET 字段1=值1,字段2=值2,... WHERE 条件

Among them, SET is followed by the fields and their values ​​that need to be modified, and WHERE is followed by the conditions that are met. For example, to change the "age" field of a user whose "name" field is "Tom" in the "users" table to "25", you can use the following code:

UPDATE users SET age=25 WHERE name='Tom';

At this time, MySQL will Returns the number of successfully modified records.

2. Update multiple pieces of data

When you need to change multiple records at the same time, you can use the following syntax:

UPDATE 表名 SET 字段1=值1, 字段2=值2,... WHERE 条件

The basic structure of this statement and the syntax for updating a single piece of data The same, except that the batch change condition needs to be added to the WHERE condition. For example, to change the users whose "age" field is greater than "20" in the "users" table and change the "name" field to "John", you can use the following code:

UPDATE users SET name='John' WHERE age>20;

At this time, MySQL will return a successful modification Records.

3. Update multiple fields

When updating multiple fields, you need to follow SET with all the fields to be changed and the corresponding new values. For example, to change the "age" field of the user whose "name" field is "Lucy" in the "users" table to "20" and the "gender" field to "female", you can use the following code:

UPDATE users SET age=20, gender='female' WHERE name='Lucy';

At this time, MySQL will return the number of successfully modified records.

4. Change the table structure

When you need to change the table structure, you can use the ALTER TABLE statement provided by MySQL to operate. This statement can add, modify, or delete columns in the table, and can also add constraints to the table, etc. For example, to add a column named "address" to the "users" table, you can use the following code:

ALTER TABLE users ADD COLUMN address VARCHAR(100);

At this time, MySQL will return "OK", indicating that the addition is successful.

5. Delete data

In MySQL, you can use the DELETE statement to delete specified data. The basic syntax of the DELETE statement is as follows:

DELETE FROM 表名 WHERE 条件

Among them, FROM is followed by the name of the table to be deleted, and WHERE is followed by the conditions of the data rows that need to be deleted. For example, to delete all users whose "gender" field is "male" in the "users" table, you can use the following code:

DELETE FROM users WHERE gender='male';

At this time, MySQL will return the number of successfully deleted records.

3. Summary

MySQL is a powerful database management system that can achieve fast and efficient data operation and management. By using the SQL language, you can add, delete, modify and other operations on data in MySQL. This article introduces various ways to modify data in MySQL and hopes to be helpful to readers. In actual operation, you need to choose the appropriate method according to the actual situation, and pay attention to backing up data to prevent data loss.

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