DDL概念

DDL

数据库模式定义语言 DDL (Data Definition Language)，是用于描述数据库中要存储的现实世界实体的语言。一个数据库模式包含该数据库中全部实体的描述定义。

这些定义包括结构定义、操做方法定义等。

数据库模式定义语言并不是程序设计语言，DDL数据库模式定义语言是SQL语言（结构化程序设计语言）的组成部分。

SQL语言包括四种主要程序设计语言类别的语句：数据定义语言(DDL)，数据操做语言(DML)，数据控制语言(DCL)和事务控制语言（TCL）。

常见的DDL语句

CREATE DATABASE

建立数据库

CREATE {DATABASE | SCHEMA} db_name

[create_specification [, create_specification] ...]

create_specification:

[DEFAULT] CHARACTER SET charset_name

| [DEFAULT] COLLATE collation_name

CREATE TABLE

建立数据库表格

CREATE [TEMPORARY] TABLE tbl_name

[(create_definition,...)]

[table_options] [select_statement]

ALTER TABLE

修改数据库表格

ALTER TABLE tbl_name

alter_specification [, alter_specification] ...

alter_specification:

ADD [COLUMN] column_definition [FIRST | AFTER col_name ]

| ADD [COLUMN] (column_definition,...)

| ADD INDEX (index_col_name,...)

| ADD [CONSTRAINT [symbol]]

PRIMARY KEY (index_col_name,...)

| ADD [CONSTRAINT [symbol]]

UNIQUE (index_col_name,...)

| ADD (index_col_name,...)

| ADD [CONSTRAINT [symbol]]

FOREIGN KEY (index_col_name,...)

[reference_definition]

| ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}

| CHANGE [COLUMN] old_col_name column_definition

[FIRST|AFTER col_name]

| MODIFY [COLUMN] column_definition [FIRST | AFTER col_name]

| DROP [COLUMN] col_name

| DROP PRIMARY KEY

| DROP INDEX index_name

| DROP FOREIGN KEY fk_symbol

| DISABLE KEYS

| ENABLE KEYS

| RENAME [TO] new_tbl_name

| ORDER BY col_name

| CONVERT TO CHARACTER SET charset_name [COLLATE collation_name]

| [DEFAULT] CHARACTER SET charset_name [COLLATE collation_name]

| DISCARD TABLESPACE

| IMPORT TABLESPACE

| table_options

DROP TABLE

删除数据库表格

DROP [TEMPORARY] TABLE

tbl_name [, tbl_name] ...

[RESTRICT | CASCADE]

CREATE VIEW

建立查询命令

CREATE [OR REPLACE] [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]

VIEW view_name [(column_list)]

AS select_statement

[WITH [CASCADED | LOCAL] CHECK OPTION]

ALTER VIEW

修改查询命令

ALTER [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]

VIEW view_name [(column_list)]

AS select_statement

[WITH [CASCADED | LOCAL] CHECK OPTION]

DROP VIEW

删除查询命令

DROP VIEW

view_name [, view_name] ...

[RESTRICT | CASCADE]

TRUNCATE TABLE

删除数据表内容

TRUNCATE TABLE name [DROP/REUSE STORAGE]

DROP STORAGE：显式指明释放数据表和索引的空间

REUSE STORAGE：显式指明不释放数据表和索引的空间