MySQL学习笔记三：库和表的管理

1.MySQL数据库服务配置好后，系统会有4个默认的数据库。

　　information_schema：虚拟对象，其对象都保存在内存中

　　performance_schema：服务器性能指标库

　　mysql：记录用户权限，帮助，日志等信息

　　test：测试库

查看当前的所有数据库：

show databases   //只显示当前用户拥有权限访问的所有数据库

删除数据库

drop database if exists db_name 

创建数据库

create database if not exist db_name

在操作返回的结果中有ERROR,WARNING，可用以下语句来查看

show errors  or show warnings

查看数据库的创建脚本

show create database db_name or
select * from scheme_information.schemata

选定数据库

use mysql

查看某库中的所有表

show tables

表的创建，语法如下：

Syntax:
CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    (create_definition,...)
    [table_options]
    [partition_options]

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    [(create_definition,...)]
    [table_options]
    [partition_options]
    select_statement

Or:

CREATE [TEMPORARY] TABLE [IF NOT EXISTS] tbl_name
    { LIKE old_tbl_name | (LIKE old_tbl_name) }

下面以student为表名来创建表

use test;
create table if not exists student(
id int not null primary key auto_increment,
sno char(11) not null unique,
sname varchar(50) not null
);

查看表的结构

desc student(tbl_name)

查看表的创建脚本

show create table student(tbl_name)

查看表的状态信息

show table status like 'student'

修改表的结构，使用ALTER命令，语法：

Syntax:
ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name
    [alter_specification [, alter_specification] ...]
    [partition_options]

alter_specification:
    table_options
  | ADD [COLUMN] col_name column_definition
        [FIRST | AFTER col_name ]
  | ADD [COLUMN] (col_name column_definition,...)
  | ADD {INDEX|KEY} [index_name]
        [index_type] (index_col_name,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]] PRIMARY KEY
        [index_type] (index_col_name,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]]
        UNIQUE [INDEX|KEY] [index_name]
        [index_type] (index_col_name,...) [index_option] ...
  | ADD FULLTEXT [INDEX|KEY] [index_name]
        (index_col_name,...) [index_option] ...
  | ADD SPATIAL [INDEX|KEY] [index_name]
        (index_col_name,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]]
        FOREIGN KEY [index_name] (index_col_name,...)
        reference_definition
  | ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
  | CHANGE [COLUMN] old_col_name new_col_name column_definition
        [FIRST|AFTER col_name]
  | MODIFY [COLUMN] col_name column_definition
        [FIRST | AFTER col_name]
  | DROP [COLUMN] col_name
  | DROP PRIMARY KEY
  | DROP {INDEX|KEY} index_name
| DROP FOREIGN KEY fk_symbol
| MAX_ROWS = rows
| DISABLE KEYS
| ENABLE KEYS
| RENAME [TO|AS] new_tbl_name
| ORDER BY col_name [, col_name] ...
| CONVERT TO CHARACTER SET charset_name [COLLATE collation_name]
| [DEFAULT] CHARACTER SET [=] charset_name [COLLATE [=] collation_name]
| DISCARD TABLESPACE
| IMPORT TABLESPACE
| FORCE
| ADD PARTITION (partition_definition)
| DROP PARTITION partition_names
| TRUNCATE PARTITION {partition_names | ALL}
| COALESCE PARTITION number
| REORGANIZE PARTITION [partition_names INTO (partition_definitions)]
| ANALYZE PARTITION {partition_names | ALL}
| CHECK PARTITION {partition_names | ALL}
| OPTIMIZE PARTITION {partition_names | ALL}
| REBUILD PARTITION {partition_names | ALL}
| REPAIR PARTITION {partition_names | ALL}
| PARTITION BY partitioning_expression

例如

alter table student add (sgender int(1) not null)  -----增加列------
alter table student modify (sname varchar(100) not null)  -----修改列------
alter table student drop sno  -----删除列------

锁定表为只读

lock table student read only   ----锁定单表---
flush tables with read lock      ----锁定所有表

解锁表

unlock tables

删除表

drop table if exists student

清空表

truncate table student

表的重命名

rename table student to new_student
---------------可以使用rename进行数据库的移动---------------
rename table test.student to test1.stduent