PHP development basic tutorial structure definition statement
Introduction
DDL is a data definition language. Simply put, it is a language for creating, deleting, modifying and operating databases, data tables, and data fields. , the biggest difference between it and data operation statements (DML) is that DML (data operation statements) operate on the internal data of the table, and do not involve the definition of the table, modification of the structure, or other objects.
In this chapter, we divided it into three parts when explaining this section:
Database operation
Data table operation
Data field operations
##Database operations
1.Create database
Example:
Click to execute, and there will be an additional php database on the right
2View database
##Category
Detailed explanation
Basic syntax
create database database name;
Example
create database php ;
Example description
Create a database, the name of the database is php
## Category
Detailed explanation
Basic syntax
show databases;
Example description
Show all databases of the current server
##Note:show refers to displaydatabase refers to the database databases is the plural form of database, referring to all databases.
Enter show databases; the display is as follows
##3. Select the database
Basic syntax:
#Category
Detailed explanation
Basic syntax
use library name;
Example
use php;
Example description
Using database php
Note: Use refers to use; library name is the name of the specific database in the current database system;
# Note: We can use the USE statement to switch the database to be operated at any time
## 4. View tables in the database
# After entering the library, we can see how many data tables in this library.
Category
Detailed explanation
Basic syntax
show tables;
# Example Example
## Show all the tables under the current database
##
After using use to enter a database, you can use show tables
Example to view the tables of the current database:
Note: The database must be selected before you can view the table
5. Delete database
Note: Drop is Chinese that can be translated as a finger. ## Note: After the database is deleted, all the following data will be deleted, so you must carefully and make a corresponding backup before deleting.
#1. Create table
##Category
Detailed explanation
Basic syntax
drop database library name;
Example
## drop database liwenkai;
Example description
Delete a database, the name of the database is liwenkai
##Q##Category
Detailed explanation
##Basic syntax
create table table name (field name 1 field type,.... field name n field type n);
Create a table named user, the first field is username, the field type of the table is varchar, the length is 32 length. The second field is password, the type is also varchar, and the length is also 32 characters.
Note:
In order to better let everyone get started, data types are temporarily outside the scope of our explanation in this chapter. I’m afraid that everyone will focus on one thing and lose another. It is very important to quickly learn the management and operation statements of the database. Data types, fields, character sets, and engines are all knowledge points to understand.
. As for field types, you only need to learn int now, which represents integer type. float represents floating point. char and varchar can represent strings.
We can add the length after the type, such as: varchar(20).
View table field structure information
2. Delete table
Category
Detailed explanation
Basic syntax
desc table name;
##Example
desc emp
Example description
View the table structure of the emp table
Note: Delete the table. Both tables and data will be lost. Do not delete the data before the important table.
3.Specify table engine and character set
## At the end of the creation table, we often use MyISAM or InnoDB engine. When designated by the engine, we can use:
ENGINE = InnoDB
Speculating Form default character set:
DEFAULT CHARSET = UTF8
Useraaname Varchar (10) Default Null,
)
## database field operation
#qian directly uses PHPMYADMIN to create the field in the table# Click the structure:
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## The effect is as follows:Create Table Emp (Password Date Default Null,Deleting or modifying fields is also done in phpAdmin. You can try it yourself
# Note: We can use the USE statement to switch the database to be operated at any time
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