MySQL Data Definition Language DDL

Keyword

• Created: CREATE
• Modify: ALTER
• Delete: DROP

Management Library

Create a library

• grammar

CREATE DATABASE 库名;

• Creating students Library

CREATE DATABASE students;
#更安全的做法
CREATE DATABASE IF NOT EXISTS students;

Modify the library

• Change the default character set

ALTER DATABASE students CHARACTER SET  gbk;

Delete library

• Delete students Library

DROP DATABASE students;
#更安全的做法
DROP DATABASE IF EXISTS students;

Management table

Create a table

• grammar

CREATE TABLE 表名(
    列名 类型
    ...
    列名 类型
    约束
);

• Case

#建立一个account表
CREATE TABLE account (
    account_number char(10),
    branch_name char(30)  NOT  NULL,
    balance  numeric(12.2),
    PRIMARY KEY (account_number),
    FOREIGN KEY (branch_name) 
    REFERENCES branch(branch_name), 
    CONSTRAINT chk_balance CHECK (balance >= 0 )
) ;

Unbridled default value == NULL, any value can be thought == NULL

Modify table

• Modify the column name

  • grammar

  ALTER TABLE 表名 CHANGE COLUMN(可忽略) 原列名 新列名 新类型;

  • Examples

  ALTER TABLE book CHANGE COLUMN publishdate pubdate DATETIME;

• Constraints or modify the type of a column

  • grammar

  ALTER TABLE 表名 MODIFY 列名 新类型或约束;

  • Examples

  ALTER TABLE book MODIFY pubdate DATETIME;

• Add a new column

  • grammar

  ALTER TABLE 表名 ADD COLUMN 新列名 类型;

  • Examples

  ALTER TABLE book ADD COLUMN author VARCHAR(20);

• Remove Columns

  • grammar

  ALTER TABLE 表名 DROP COLUMN 列名;

  • Examples

  ALTER TABLE book DROP COLUMN author;

• Modify the table name

  • grammar

  ALTER TABLE 表名 RENAME TO 新表名;

  • Examples

  ALTER TABLE book RENAME TO books;

Delete table

DROP TABLE IF EXISTS 表名;

Copy the table

• Replicated

#创建copy表,copy表和author表结构相同
CREATE TABLE copy LIKE author;

• Full copy

CREATE TABLE copy
SELECT * FROM author;