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SQL is a very important programming language for operating relational databases.

Since structure query language is a language that can be programmed naturally, the classification of SQL can be divided into DDL,DML,DCL according to different operating objects.

We operate databases such as create, add, update, delete operations, such as operation tables, are defined.

So DDL is the SQL definition language.

We want to use the database to store data, naturally there is a library, then tables, and then data, so we have to define the library, define the table.

1. Create a database

Create database db_name [database options] in general, options can be left unfilled.

For example, we create a student bank:

Create database student

PS: when creating a database, the command rules for the database name should follow the following rules:

A, the command should follow the rules of identifiers, that is, letters, numbers and underscores.

B. Database names must not use keywords or special symbols built into the system.

C. if you use special symbols or Chinese symbols, put'``in reverse quotation marks.

Such as creating a Chinese database:

Create database `Student Bank'

Then when we create the database, we will automatically generate a directory under the data directory with the database name and a .opt file, which is the options file for the database and stores the option information for the database. If we do not write the library when we create the database, the option is the default option.

We notice that if we use special symbols to create the database, we use other encoded characters instead of garbled characters when creating the directory. We look at the database results as follows:

So please do not mistakenly think that this is garbled, this is a wrong understanding. Of course, it is recommended to create a database and try to follow the rules of identifiers to name them.

When we define the database, we do not specify the corresponding library options, but actually the character encoding of the library and the proofreading rules of the characters. Next, let's use how to define it:

Create database `teacher` character set utf8

The options file for us to open the database is shown below:

Next, let's look at what databases are in the database server.

Query instruction: show databases

View database creation information: show create database db_name

These two query instructions are very simple, show databases is to query which databases, and show create database db_name is to look at the database creation information.

The database is created, and sometimes we don't want it, so we delete the database.

Delete instruction: drop database db_name

Or: drop database if exists db_name

The second instruction is to check whether the library exists when it is deleted, delete it if it exists, and will not report an error when there is no deletion.

Modify the database:

You can modify library options such as character encoding

Alter database db_name character set gbk

So how to change the database name? The rename recommand directive is supported in the early database version, but it is no longer supported in the current version. If we want to update the database name, there are two solutions:

1. Update the database directory name under the data directory directly

2. Create a new database, then copy the table of the current library to the new database, and then delete it. The update of the data name is completed.

The above is the operation of creating, deleting, viewing and updating the database.

Add that if we have many databases in our database server, we can also do this when we retrieve them:

Show databases like'% xx' where% is equivalent to any character, string name ending in XX

The operation of the data table and the following knowledge points will be written according to the time situation. Welcome all kinds of friends' advice.

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