Table of Contents
说明1:insert的语法说明(注意加红色的关键字)
说明2:使用DEFAULT关键字的说明
插入数据前替换NULL为数据表默认值的方法
步骤1: 使用SHOW COLUMNS取出数据表字段的默认值
步骤2,插入数据前替换其中的NULL为字典存放的默认值
Home Database Mysql Tutorial MYSQL向数据表插入默认字段值的方法

MYSQL向数据表插入默认字段值的方法

Jun 07, 2016 pm 04:37 PM
mysql Field insert data sheet method design default

数据表设计过程中很多时候会设定字段的默认值,那么向该表插入数据时会出现以下情况: 情况1:如果该字段为NULL类型,那么直接将NULL插入到该字段,字段值就自动变成了设定的默认值; 情况2:如果该字段为NOT NULL类型,那么直接将NULL插入到该字段的话,在

数据表设计过程中很多时候会设定字段的默认值,那么向该表插入数据时会出现以下情况:

情况1:如果该字段为NULL类型,那么直接将NULL插入到该字段,字段值就自动变成了设定的默认值;

情况2:如果该字段为NOT NULL类型,那么直接将NULL插入到该字段的话,在普通模式下该字段的值会变成默认值并发出警告,但是strict模式下会直接报错;

对于情况2的解决方法是:使用DEFAULT关键词。

官方文档(地址)中对此有了说明:

说明1:insert的语法说明(注意加红色的关键字)

INSERT [LOW_PRIORITY | DELAYED | HIGH_PRIORITY] [IGNORE]
[INTO] tbl_name
[PARTITION (partition_name,...)]
[(col_name,...)]
{VALUES | VALUE} ({expr | DEFAULT},…),(…),…
[ ON DUPLICATE KEY UPDATE
col_name=expr
[, col_name=expr] … ]

说明2:使用DEFAULT关键字的说明

Use the keyword DEFAULT to set a column explicitly to its default value. This makes it easier to write INSERTstatements that assign values to all but a few columns, because it enables you to avoid writing an incompleteVALUES list that does not include a value for each column in the table. Otherwise, you would have to write out the list of column names corresponding to each value in the VALUES list.

翻译过来大致就是说,用关键字“DEFAULT”可以显式的在insert的过程中将一个字段设定为它的默认值。
比如一条SQL可以是这样的:insert into student(sno,sname,sage,class) values(1, ‘crazyant’, ’25′, DEFAULT),这时候就直接将班级class的默认值插入进去了。

然而使用load data infile to db,即直接将文件导入到数据表时,却无法使用默认的DEFAULT值,因为将该字段设定为”DEFAULT”会被认为是个字符串,改成NULL(用\N)表示则又会出现将NULL插入到NOT NULL的错误。

?还有一种方法是程序自动取出数据表的默认值,然后在插入数据之前,自动将数据中的NULL值替换成数据表该字段的默认值,如下步骤所示:

插入数据前替换NULL为数据表默认值的方法

步骤1: 使用SHOW COLUMNS取出数据表字段的默认值
mysql> SHOW COLUMNS FROM City;
+------------+----------+------+-----+---------+----------------+
| Field      | Type     | Null | Key | Default | Extra          |
+------------+----------+------+-----+---------+----------------+
| Id         | int(11)  | NO   | PRI | NULL    | auto_increment |
| Name       | char(35) | NO   |     |        |                |
| Country    | char(3)  | NO   | UNI | -1      |                |
| District   | char(20) | YES  | MUL |         |                |
| Population | int(11)  | NO   |     | 0       |                |
+------------+----------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
Copy after login

如上所示,第5列”Default”下的这一列就是数据表字段的默认值,我们可以取出第一列和第五列,放在一个数组或字典里面:

array[id]=NULL
array[Name]=”"
array[Country]=-1
array[District]=”"
array[Population]=0

步骤2,插入数据前替换其中的NULL为字典存放的默认值

在插入数据表之前,如果某个字段的值为NULL,就根据字段名从上述字典取出默认值,替换掉NULL,然后再插入数据。

这种方法在load data from file中可用,因为load data的效率比insert的效率高太多,所以值得这么做。

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

How to open phpmyadmin How to open phpmyadmin Apr 10, 2025 pm 10:51 PM

You can open phpMyAdmin through the following steps: 1. Log in to the website control panel; 2. Find and click the phpMyAdmin icon; 3. Enter MySQL credentials; 4. Click "Login".

MySQL: An Introduction to the World's Most Popular Database MySQL: An Introduction to the World's Most Popular Database Apr 12, 2025 am 12:18 AM

MySQL is an open source relational database management system, mainly used to store and retrieve data quickly and reliably. Its working principle includes client requests, query resolution, execution of queries and return results. Examples of usage include creating tables, inserting and querying data, and advanced features such as JOIN operations. Common errors involve SQL syntax, data types, and permissions, and optimization suggestions include the use of indexes, optimized queries, and partitioning of tables.

MySQL's Place: Databases and Programming MySQL's Place: Databases and Programming Apr 13, 2025 am 12:18 AM

MySQL's position in databases and programming is very important. It is an open source relational database management system that is widely used in various application scenarios. 1) MySQL provides efficient data storage, organization and retrieval functions, supporting Web, mobile and enterprise-level systems. 2) It uses a client-server architecture, supports multiple storage engines and index optimization. 3) Basic usages include creating tables and inserting data, and advanced usages involve multi-table JOINs and complex queries. 4) Frequently asked questions such as SQL syntax errors and performance issues can be debugged through the EXPLAIN command and slow query log. 5) Performance optimization methods include rational use of indexes, optimized query and use of caches. Best practices include using transactions and PreparedStatemen

Why Use MySQL? Benefits and Advantages Why Use MySQL? Benefits and Advantages Apr 12, 2025 am 12:17 AM

MySQL is chosen for its performance, reliability, ease of use, and community support. 1.MySQL provides efficient data storage and retrieval functions, supporting multiple data types and advanced query operations. 2. Adopt client-server architecture and multiple storage engines to support transaction and query optimization. 3. Easy to use, supports a variety of operating systems and programming languages. 4. Have strong community support and provide rich resources and solutions.

How to connect to the database of apache How to connect to the database of apache Apr 13, 2025 pm 01:03 PM

Apache connects to a database requires the following steps: Install the database driver. Configure the web.xml file to create a connection pool. Create a JDBC data source and specify the connection settings. Use the JDBC API to access the database from Java code, including getting connections, creating statements, binding parameters, executing queries or updates, and processing results.

How to start mysql by docker How to start mysql by docker Apr 15, 2025 pm 12:09 PM

The process of starting MySQL in Docker consists of the following steps: Pull the MySQL image to create and start the container, set the root user password, and map the port verification connection Create the database and the user grants all permissions to the database

Centos install mysql Centos install mysql Apr 14, 2025 pm 08:09 PM

Installing MySQL on CentOS involves the following steps: Adding the appropriate MySQL yum source. Execute the yum install mysql-server command to install the MySQL server. Use the mysql_secure_installation command to make security settings, such as setting the root user password. Customize the MySQL configuration file as needed. Tune MySQL parameters and optimize databases for performance.

MySQL's Role: Databases in Web Applications MySQL's Role: Databases in Web Applications Apr 17, 2025 am 12:23 AM

The main role of MySQL in web applications is to store and manage data. 1.MySQL efficiently processes user information, product catalogs, transaction records and other data. 2. Through SQL query, developers can extract information from the database to generate dynamic content. 3.MySQL works based on the client-server model to ensure acceptable query speed.

See all articles