数据库上手避坑之--sql基础从安装到数据引擎

1、安装mariadb

　　sudo  pacman  -S  mariadb

2、启动mariadb的服务

　　systemctl start  mariadb

3、应用root连接到服务器

　　mysql -u sqlxxl -p

　　Enter password:输入自己的密码

4、第零屏说明：

Welcome to the MariaDB monitor.  Commands end with ; or g.
Your MariaDB connection id is 3
Server version: 10.5.8-MariaDB Arch Linux

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or 'h' for help. Type 'c' to clear the current input statement.

MariaDB [(none)]> 

 　　1）：第1行是欢迎信息，命令行以“;”结尾或者以“”g结尾

　　2）：第2行表明本次连接的标识号是3，若出现问题时才需要

　　3）：第3行表明Mariadb的版本号时：10.5.8

　　4）：第5行展示了版权信息

　　5）：第7行展示如何获取帮助信息，如何清除输出信息

5、帮助信息：

MariaDB [(none)]> help

General information about MariaDB can be found at
http://mariadb.org

List of all client commands:
Note that all text commands must be first on line and end with ';'
?         (?) Synonym for `help'.
clear     (c) Clear the current input statement.
connect   (
) Reconnect to the server. Optional arguments are db and host.
delimiter (d) Set statement delimiter.
edit      (e) Edit command with $EDITOR.
ego       (G) Send command to MariaDB server, display result vertically.
exit      (q) Exit mysql. Same as quit.
go        (g) Send command to MariaDB server.
help      (h) Display this help.
nopager   (
) Disable pager, print to stdout.
notee     (	) Don't write into outfile.
pager     (P) Set PAGER [to_pager]. Print the query results via PAGER.
print     (p) Print current command.
prompt    (R) Change your mysql prompt.
quit      (q) Quit mysql.
rehash    (#) Rebuild completion hash.
source    (.) Execute an SQL script file. Takes a file name as an argument.
status    (s) Get status information from the server.
system    (!) Execute a system shell command.
tee       (T) Set outfile [to_outfile]. Append everything into given outfile.
use       (u) Use another database. Takes database name as argument.
charset   (C) Switch to another charset. Might be needed for processing binlog with multi-byte charsets.
warnings  (W) Show warnings after every statement.
nowarning (w) Don't show warnings after every statement.

For server side help, type 'help contents'

MariaDB [(none)]> help contents
You asked for help about help category: "Contents"
For more information, type 'help <item>', where <item> is one of the following
categories:
   Account Management
   Administration
   Compound Statements
   Data Definition
   Data Manipulation
   Data Types
   Functions
   Functions and Modifiers for Use with GROUP BY
   Geographic Features
   Help Metadata
   Language Structure
   Plugins
   Procedures
   Sequences
   Table Maintenance
   Transactions
   User-Defined Functions
   Utility

MariaDB [(none)]> help Data Manipulation
You asked for help about help category: "Data Manipulation"
For more information, type 'help <item>', where <item> is one of the following
topics:
   CALL
   Concurrent Inserts
   DELETE
   DO
   DUAL
   EXCEPT
   FOR UPDATE
   GROUP BY
   HANDLER Commands
   HIGH_PRIORITY and LOW_PRIORITY
   IGNORE
   INSERT
   INSERT - Default &amp; Duplicate Values
   INSERT DELAYED
   INSERT IGNORE
   INSERT ON DUPLICATE KEY UPDATE
   INSERT SELECT
   INTERSECT
   JOIN Syntax
   LIMIT
   LOAD DATA INFILE
   LOAD XML
   LOCK IN SHARE MODE
   Non-Recursive Common Table Expressions Overview
   ORDER BY
   PROCEDURE
   REPLACE
   Recursive Common Table Expressions Overview
   SELECT
   SELECT INTO DUMPFILE
   SELECT INTO OUTFILE
   SELECT WITH ROLLUP
   UNION
   UPDATE
   WITH

MariaDB [(none)]> help SHOW DATABASES
Name: 'SHOW DATABASES'
Description:
Syntax
------ 
SHOW {DATABASES | SCHEMAS}
 [LIKE 'pattern' | WHERE expr]
 
Description
----------- 
SHOW DATABASES lists the databases on the MariaDB server
host.
SHOW SCHEMAS is a synonym for 
SHOW DATABASES. The LIKE clause, if
present on its own, indicates which database names to match.
The WHERE and LIKE clauses can be given to select rows using
more general conditions, as discussed in Extended SHOW.
 
You see only those databases for which you have some kind of
privilege, unless you have the global 
SHOW DATABASES privilege. You
can also get this list using the mysqlshow command.
 
If the server was started with the --skip-show-database
option, you cannot use this statement at all unless you have
the
SHOW DATABASES privilege.
 
Example
 
SHOW DATABASES;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
 
SHOW DATABASES LIKE 'm%';
+---------------+
| Database (m%) |
+---------------+
| mysql |
+---------------+ 

URL: https://mariadb.com/kb/en/library/show-databases/

6、数据库基本操作：

　　几个约定：

　　1)、mysql命令是不区分大小写的

　　2)、mysql中数据库、表名、属性名都是需要区分大小写

　　常见操作：

　　1)、查看系统中数据库　　

　　2)、创建数据库　　

　　3)、删除数据库

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| student_info       |
+--------------------+
4 rows in set (0.040 sec)

MariaDB [(none)]> create database sample;
Query OK, 1 row affected (0.001 sec)

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| sample             |
| student_info       |
+--------------------+
5 rows in set (0.001 sec)

MariaDB [(none)]> drop database sample;
Query OK, 0 rows affected (0.036 sec)

MariaDB [(none)]> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
| performance_schema |
| student_info       |
+--------------------+
4 rows in set (0.001 sec)

7、数据库存储引擎,查看数据库引擎,数据库引擎的特点

MariaDB [(none)]> help show engines;
Name: 'SHOW ENGINES'
Description:
Syntax
------ 
SHOW [STORAGE] ENGINES
 
Description
----------- 
SHOW ENGINES displays status information about the server's
storage engines. This is particularly useful for checking
whether a storage
engine is supported, or to see what the default engine is. 
SHOW TABLE TYPES is a deprecated synonym.
 
The information_schema.ENGINES table provides the same
information.
 
Since storage engines are plugins, different information
about them is also shown in the information_schema.PLUGINS
table and by the SHOW PLUGINS statement.
 
Note that both MySQL's InnoDB and Percona's XtraDB
replacement are labeled as InnoDB. However, if XtraDB is in
use, it will be specified in the COMMENT field. See XtraDB
and InnoDB. The same applies to FederatedX.
 
The output consists of the following columns:
Engine indicates the engine's name.
Support indicates whether the engine is installed, and
whether it is the default engine for the current session.
Comment is a brief description.
Transactions, XA and Savepoints indicate whether
transactions, XA transactions and transaction savepoints are
supported by the engine.
 
Examples
-------- 
SHOW ENGINESG
*************************** 1. row
***************************
 Engine: InnoDB
 Support: DEFAULT
 Comment: Supports transactions, row-level locking, and
foreign keys
Transactions: YES
 XA: YES
 Savepoints: YES
*************************** 2. row
***************************
 Engine: CSV
 Support: YES
 Comment: CSV storage engine
Transactions: NO
 XA: NO
 Savepoints: NO
*************************** 3. row
***************************
 Engine: MyISAM
 Support: YES
 Comment: MyISAM storage engine
Transactions: NO
 XA: NO
 Savepoints: NO
*************************** 4. row
***************************
 Engine: BLACKHOLE
 Support: YES
 Comment: /dev/null storage engine (anything you write to it
disappears)
Transactions: NO
 XA: NO
 Savepoints: NO
*************************** 5. row
***************************
 Engine: FEDERATED
 Support: YES
 Comment: FederatedX pluggable storage engine
Transactions: YES
 XA: NO
 Savepoints: YES
*************************** 6. row
***************************
 Engine: MRG_MyISAM
 Support: YES
 Comment: Collection of identical MyISAM tables
Transactions: NO
 XA: NO
 Savepoints: NO
*************************** 7. row
***************************
 Engine: ARCHIVE
 Support: YES
 Comment: Archive storage engine
Transactions: NO
 XA: NO
 Savepoints: NO
*************************** 8. row
***************************
 Engine: MEMORY
 Support: YES
 Comment: Hash based, stored in memory, useful for temporary
tables
Transactions: NO
 XA: NO
 Savepoints: NO
*************************** 9. row
***************************
 Engine: PERFORMANCE_SCHEMA
 Support: YES
 Comment: Performance Schema
Transactions: NO
 XA: NO
 Savepoints: NO
*************************** 10. row
***************************
 Engine: Aria
 Support: YES
 Comment: Crash-safe tables with MyISAM heritage
Transactions: NO
 XA: NO
 Savepoints: NO
10 rows in set (0.00 sec)

　　MyISAM：需要临时存放数据；数据量不大，数据安全不高时；

　　MEMORY：需要很高的处理效率，表主要用来插入和查询记录时；

　　InnoDB：　需要提交、回滚和崩溃恢复能力的事务安全；需要并发控制时