MySQL的介绍和基本应用

一、概念

1、数据库

  DB 数据库（Database），存储数据的仓库，它保存一系列有组织的数据库。
  DBMS 数据库管理系统（Database Management System），数据库是通过 DBMS 创建和操作的容器。

2、SQL

  SQL 结构化查询语言（Structure Query Language），专门用来与数据库通信的语言。SQl 不是某个特定数据库供应商专有的语言，几乎所有的 DBMS 都支持 SQL。
  DDL 数据定义语言，用来定义数据库对象：数据库，表，列等等。关键字：create，alter，drop 等。
  DML 数据操作语言，用来对数据库中表中的记录进行操作。关键字：insert，delete，update 等。
  DCL 数据控制语言，用来定义数据库的访问权限，安全级别等。
  DQL 数据查询语言，用来查询数据库的记录，关键字：select，from，where 等。

二、配置文件

   MySQL 的配置文件是 my.imi，我们只需要对 mysqld 下面的配置进行操作，修改后必须重启 MySQL 才会生效。

# 我的 my.imi 的配置
[client]

# pipe=

# socket=MYSQL

port=3306

[mysql]
no-beep

# default-character-set=

# SERVER SECTION
# ----------------------------------------------------------------------
#
# The following options will be read by the MySQL Server. Make sure that
# you have installed the server correctly (see above) so it reads this 
# file.
#
# server_type=3
# mysqld是关于mysql服务器端的配置
[mysqld]

# The next three options are mutually exclusive to SERVER_PORT below.
# skip-networking
# enable-named-pipe
# shared-memory

# shared-memory-base-name=MYSQL

# The Pipe the MySQL Server will use
# socket=MYSQL

# The TCP/IP Port the MySQL Server will listen on
# MySQL启动后占用的端口号，默认是3306
port=3306

# Path to installation directory. All paths are usually resolved relative to this.
# MySQL的安装路径
# basedir="C:/Program Files/MySQL/MySQL Server 8.0/"

# Path to the database root
# MySQL的数据存储路径
datadir=C:/ProgramData/MySQL/MySQL Server 8.0/Data

# The default character set that will be used when a new schema or table is
# created and no character set is defined
# character-set-server=

# The default authentication plugin to be used when connecting to the server
default_authentication_plugin=caching_sha2_password

# The default storage engine that will be used when create new tables when
# 数据库存储引擎
default-storage-engine=INNODB

# Set the SQL mode to strict
# 语法模式
sql-mode="STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION"

# General and Slow logging.
log-output=FILE
general-log=0
general_log_file="LAPTOP-MJQ1613H.log"
slow-query-log=1
slow_query_log_file="LAPTOP-MJQ1613H-slow.log"
long_query_time=10

# Binary Logging.
log-bin="LAPTOP-MJQ1613H-bin"

# Error Logging.
log-error="LAPTOP-MJQ1613H.err"

# Server Id.
server-id=1

# Indicates how table and database names are stored on disk and used in MySQL.
# Value = 0: Table and database names are stored on disk using the lettercase specified in the
#            CREATE TABLE or CREATE DATABASE statement. Name comparisons are case sensitive.
#            You should not set this variable to 0 if you are running MySQL on a system that has
#            case-insensitive file names (such as Windows or macOS).
# Value = 1: Table names are stored in lowercase on disk and name comparisons are not
#            case-sensitive. MySQL converts all table names to lowercase on storage and lookup.
#            This behavior also applies to database names and table aliases.
# Value = 3, Table and database names are stored on disk using the lettercase specified in the
#            CREATE TABLE or CREATE DATABASE statement, but MySQL converts them to lowercase on
#            lookup. Name comparisons are not case sensitive. This works only on file systems
#            that are not case-sensitive! InnoDB table names and view names are stored in
#            lowercase, as for Value = 1.
# NOTE: lower_case_table_names can only be configured when initializing the server.
#       Changing the lower_case_table_names setting after the server is initialized is prohibited.
lower_case_table_names=1

# Secure File Priv.
secure-file-priv="C:/ProgramData/MySQL/MySQL Server 8.0/Uploads"

# The maximum amount of concurrent sessions the MySQL server will
# allow. One of these connections will be reserved for a user with
# SUPER privileges to allow the administrator to login even if the
# connection limit has been reached.
# MySQL 的最大连接数
max_connections=500

# The number of open tables for all threads. Increasing this value
# increases the number of file descriptors that mysqld requires.
# Therefore you have to make sure to set the amount of open files
# allowed to at least 4096 in the variable "open-files-limit" in
# section [mysqld_safe]
table_open_cache=2000

# Maximum size for internal (in-memory) temporary tables. If a table
# grows larger than this value, it is automatically converted to disk
# based table This limitation is for a single table. There can be many
# of them.
tmp_table_size=43M

# How many threads we should keep in a cache for reuse. When a client
# disconnects, the client's threads are put in the cache if there aren't
# more than thread_cache_size threads from before.  This greatly reduces
# the amount of thread creations needed if you have a lot of new
# connections. (Normally this doesn't give a notable performance
# improvement if you have a good thread implementation.)
thread_cache_size=10

#*** MyISAM Specific options
# The maximum size of the temporary file MySQL is allowed to use while
# recreating the index (during REPAIR, ALTER TABLE or LOAD DATA INFILE.
# If the file-size would be bigger than this, the index will be created
# through the key cache (which is slower).
myisam_max_sort_file_size=100G

# If the temporary file used for fast index creation would be bigger
# than using the key cache by the amount specified here, then prefer the
# key cache method.  This is mainly used to force long character keys in
# large tables to use the slower key cache method to create the index.
myisam_sort_buffer_size=76M

# Size of the Key Buffer, used to cache index blocks for MyISAM tables.
# Do not set it larger than 30% of your available memory, as some memory
# is also required by the OS to cache rows. Even if you're not using
# MyISAM tables, you should still set it to 8-64M as it will also be
# used for internal temporary disk tables.
key_buffer_size=8M

# Size of the buffer used for doing full table scans of MyISAM tables.
# Allocated per thread, if a full scan is needed.
read_buffer_size=64K

read_rnd_buffer_size=256K

#*** INNODB Specific options ***
# innodb_data_home_dir=

# Use this option if you have a MySQL server with InnoDB support enabled
# but you do not plan to use it. This will save memory and disk space
# and speed up some things.
# skip-innodb

# If set to 1, InnoDB will flush (fsync) the transaction logs to the
# disk at each commit, which offers full ACID behavior. If you are
# willing to compromise this safety, and you are running small
# transactions, you may set this to 0 or 2 to reduce disk I/O to the
# logs. Value 0 means that the log is only written to the log file and
# the log file flushed to disk approximately once per second. Value 2
# means the log is written to the log file at each commit, but the log
# file is only flushed to disk approximately once per second.
innodb_flush_log_at_trx_commit=1

# The size of the buffer InnoDB uses for buffering log data. As soon as
# it is full, InnoDB will have to flush it to disk. As it is flushed
# once per second anyway, it does not make sense to have it very large
# (even with long transactions).
innodb_log_buffer_size=1M

# InnoDB, unlike MyISAM, uses a buffer pool to cache both indexes and
# row data. The bigger you set this the less disk I/O is needed to
# access data in tables. On a dedicated database server you may set this
# parameter up to 80% of the machine physical memory size. Do not set it
# too large, though, because competition of the physical memory may
# cause paging in the operating system.  Note that on 32bit systems you
# might be limited to 2-3.5G of user level memory per process, so do not
# set it too high.
innodb_buffer_pool_size=8M

# Size of each log file in a log group. You should set the combined size
# of log files to about 25%-100% of your buffer pool size to avoid
# unneeded buffer pool flush activity on log file overwrite. However,
# note that a larger logfile size will increase the time needed for the
# recovery process.
innodb_log_file_size=48M

# Number of threads allowed inside the InnoDB kernel. The optimal value
# depends highly on the application, hardware as well as the OS
# scheduler properties. A too high value may lead to thread thrashing.
innodb_thread_concurrency=17

# The increment size (in MB) for extending the size of an auto-extend InnoDB system tablespace file when it becomes full.
innodb_autoextend_increment=64

# The number of regions that the InnoDB buffer pool is divided into.
# For systems with buffer pools in the multi-gigabyte range, dividing the buffer pool into separate instances can improve concurrency,
# by reducing contention as different threads read and write to cached pages.
innodb_buffer_pool_instances=8

# Determines the number of threads that can enter InnoDB concurrently.
innodb_concurrency_tickets=5000

# Specifies how long in milliseconds (ms) a block inserted into the old sublist must stay there after its first access before
# it can be moved to the new sublist.
innodb_old_blocks_time=1000

# It specifies the maximum number of .ibd files that MySQL can keep open at one time. The minimum value is 10.
innodb_open_files=300

# When this variable is enabled, InnoDB updates statistics during metadata statements.
innodb_stats_on_metadata=0

# When innodb_file_per_table is enabled (the default in 5.6.6 and higher), InnoDB stores the data and indexes for each newly created table
# in a separate .ibd file, rather than in the system tablespace.
innodb_file_per_table=1

# Use the following list of values: 0 for crc32, 1 for strict_crc32, 2 for innodb, 3 for strict_innodb, 4 for none, 5 for strict_none.
innodb_checksum_algorithm=0

# The number of outstanding connection requests MySQL can have.
# This option is useful when the main MySQL thread gets many connection requests in a very short time.
# It then takes some time (although very little) for the main thread to check the connection and start a new thread.
# The back_log value indicates how many requests can be stacked during this short time before MySQL momentarily
# stops answering new requests.
# You need to increase this only if you expect a large number of connections in a short period of time.
back_log=80

# If this is set to a nonzero value, all tables are closed every flush_time seconds to free up resources and
# synchronize unflushed data to disk.
# This option is best used only on systems with minimal resources.
flush_time=0

# The minimum size of the buffer that is used for plain index scans, range index scans, and joins that do not use
# indexes and thus perform full table scans.
join_buffer_size=256K

# The maximum size of one packet or any generated or intermediate string, or any parameter sent by the
# mysql_stmt_send_long_data() C API function.
max_allowed_packet=4M

# If more than this many successive connection requests from a host are interrupted without a successful connection,
# the server blocks that host from performing further connections.
max_connect_errors=100

# Changes the number of file descriptors available to mysqld.
# You should try increasing the value of this option if mysqld gives you the error "Too many open files".
open_files_limit=4161

# If you see many sort_merge_passes per second in SHOW GLOBAL STATUS output, you can consider increasing the
# sort_buffer_size value to speed up ORDER BY or GROUP BY operations that cannot be improved with query optimization
# or improved indexing.
sort_buffer_size=256K

# The number of table definitions (from .frm files) that can be stored in the definition cache.
# If you use a large number of tables, you can create a large table definition cache to speed up opening of tables.
# The table definition cache takes less space and does not use file descriptors, unlike the normal table cache.
# The minimum and default values are both 400.
table_definition_cache=1400

# Specify the maximum size of a row-based binary log event, in bytes.
# Rows are grouped into events smaller than this size if possible. The value should be a multiple of 256.
binlog_row_event_max_size=8K

# If the value of this variable is greater than 0, a replication slave synchronizes its master.info file to disk.
# (using fdatasync()) after every sync_master_info events.
sync_master_info=10000

# If the value of this variable is greater than 0, the MySQL server synchronizes its relay log to disk.
# (using fdatasync()) after every sync_relay_log writes to the relay log.
sync_relay_log=10000

# If the value of this variable is greater than 0, a replication slave synchronizes its relay-log.info file to disk.
# (using fdatasync()) after every sync_relay_log_info transactions.
sync_relay_log_info=10000

# Load mysql plugins at start."plugin_x ; plugin_y".
# plugin_load

# The TCP/IP Port the MySQL Server X Protocol will listen on.
loose_mysqlx_port=33060

三、MySQL 的语法规范

  1、不区分大小写，但是建议关键字大写，表名，列名小写。
  2、每条语句用分号结尾。
  3、命令可以随意缩进和换行。
  4、字符型使用单引号或双引号包裹。
  5、注释
    单行注释
      # 注释文本
      -- 注释文本
    多行注释
      /* 注释文本 */

四、MySQL 的常用命令

  平时大多使用图形化界面进行操作，对 MySQL 的命令渐渐淡忘，在此进行记录。以下命名属于 MySQL 命名，不受平台限制。

1) 登录

  地址指的是 IP、域名，本机可以不写或 localhost，-P 表示端口号不写默认 3306，-u 表示用户名，-p 后回车然后输入密码。

mysql -h地址 -P3306 -uroot -p

下面的命令都是在 MySQL 命令框中执行。

2）查看版本

selcet version();

3）查看数据库

  查看 MySQL 中现在有哪些数据库。

show databases;

4）进入数据库

use 数据库名;

5）查看当前所在数据库

select database();

6）查看表

  ①查看当前数据库中有那些表

show tables;

  ②查看指定数据库中有那些表

show tables from 数据库名;

7）查看表结构

desc 表名;

8）退出MySQL 命令框

exit;

五、MySQL 的思维导图

  这也是我今后的MySQL学习路线。