DDL概念

DDL

數據庫模式定義語言 DDL (Data Definition Language)，是用於描述數據庫中要存儲的現實世界實體的語言。一個數據庫模式包含該數據庫中全部實體的描述定義。

這些定義包括結構定義、操做方法定義等。

數據庫模式定義語言並不是程序設計語言，DDL數據庫模式定義語言是SQL語言（結構化程序設計語言）的組成部分。

SQL語言包括四種主要程序設計語言類別的語句：數據定義語言(DDL)，數據操做語言(DML)，數據控制語言(DCL)和事務控制語言（TCL）。

常見的DDL語句

CREATE DATABASE

建立數據庫

CREATE {DATABASE | SCHEMA} db_name

[create_specification [, create_specification] ...]

create_specification:

[DEFAULT] CHARACTER SET charset_name

| [DEFAULT] COLLATE collation_name

CREATE TABLE

建立數據庫表格

CREATE [TEMPORARY] TABLE tbl_name

[(create_definition,...)]

[table_options] [select_statement]

ALTER TABLE

修改數據庫表格

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

刪除數據庫表格

DROP [TEMPORARY] TABLE

tbl_name [, tbl_name] ...

[RESTRICT | CASCADE]

CREATE VIEW

建立查詢命令

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

VIEW view_name [(column_list)]

AS select_statement

[WITH [CASCADED | LOCAL] CHECK OPTION]

ALTER VIEW

修改查詢命令

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

VIEW view_name [(column_list)]

AS select_statement

[WITH [CASCADED | LOCAL] CHECK OPTION]

DROP VIEW

刪除查詢命令

DROP VIEW

view_name [, view_name] ...

[RESTRICT | CASCADE]

TRUNCATE TABLE

刪除數據表內容

TRUNCATE TABLE name [DROP/REUSE STORAGE]

DROP STORAGE：顯式指明釋放數據表和索引的空間

REUSE STORAGE：顯式指明不釋放數據表和索引的空間