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Updated on 2024-05-07 GMT+08:00

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DDL Syntax Overview

Data definition language (DDL) is used to define or modify an object in a database, such as a table, an index, or a view.

GaussDB does not support DDL if its CN is unavailable. For example, if the primary node of the database is faulty, creating a database or a table will fail.

Defining a CMK

Client master keys (CMKs) are used to encrypt column encryption keys (CEKs) for the encrypted database feature. CMK definition includes creating and deleting a CMK. For details about related SQL statements, see Table 1.

**Table 1** SQL statements for defining a CMK
Function	SQL Statement
Creating a CMK	CREATE CLIENT MASTER KEY
Deleting a CMK	DROP CLIENT MASTER KEY

Defining a CEK

CEKs are used to encrypt data for the encrypted database feature. You can create a CEK, change the client master key specified by a CEK, and delete a CEK. For details about related SQL statements, see Table 1.

**Table 2** SQL statements for defining a CEK
Function	SQL Statement
Creating a CEK	CREATE COLUMN ENCRYPTION KEY
Changing the client master key specified by a CEK	8.14.191-ALTER COLUMN ENCRYPTION KEY
Deleting a CEK	DROP COLUMN ENCRYPTION KEY

Defining a Database

A database is the warehouse for organizing, storing, and managing data. Defining a database includes: creating a database, altering the database attributes, and dropping the database. For details about related SQL statements, see Table 3.

**Table 3** SQL statements for defining a database
Function	SQL Statement
Creating a database	CREATE DATABASE
Altering database attributes	ALTER DATABASE
Dropping a Database	DROP DATABASE

Defining a Schema

A schema is the set of a group of database objects and is used to control the access to the database objects. For details about related SQL statements, see Table 4.

**Table 4** SQL statements for defining a schema
Function	SQL Statement
Creating a schema	CREATE SCHEMA
Altering schema attributes	ALTER SCHEMA
Dropping a schema	DROP SCHEMA

Defining a Tablespace

A tablespace is used to manage data objects and corresponds to a catalog on a disk. For details about related SQL statements, see Table 5.

**Table 5** SQL statements for defining a tablespace
Function	SQL Statement
Creating a tablespace	CREATE TABLESPACE
Altering tablespace attributes	ALTER TABLESPACE
Dropping a tablespace	DROP TABLESPACE

Defining a Table

A table is a special data structure in a database and is used to store data objects and relationship between data objects. For details about related SQL statements, see Table 6.

**Table 6** SQL statements for defining a table
Function	SQL Statement
Creating a table	CREATE TABLE
Altering table attributes	ALTER TABLE
Dropping a table	DROP TABLE

Defining a Partitioned Table

A partitioned table is a logical table used to improve query performance and does not store data (data is stored in ordinary tables). For details about related SQL statements, see Table 7.

**Table 7** SQL statements for defining a partitioned table
Function	SQL Statement
Creating a partitioned table	CREATE TABLE PARTITION
Create a partition	ALTER TABLE PARTITION
Altering partitioned table attributes	ALTER TABLE PARTITION
Deleting a partition	ALTER TABLE PARTITION
Dropping a partitioned table	DROP TABLE

Defining an Index

An index indicates the sequence of values in one or more columns in a database table. It is a data structure that improves the speed of data access to specific information in a database table. For details about related SQL statements, see Table 8.

**Table 8** SQL statements for defining an index
Function	SQL Statement
Creating an index	CREATE INDEX
Altering index attributes	ALTER INDEX
Dropping an index	DROP INDEX
Rebuilding an index	REINDEX

Defining a Stored Procedure

A stored procedure is a set of SQL statements for achieving specific functions and is stored in the database after compiling. Users can specify a name and provide parameters (if necessary) to execute the stored procedure. For details about related SQL statements, see Table 9.

**Table 9** SQL statements for defining a stored procedure
Function	SQL Statement
Creating a stored procedure	CREATE PROCEDURE
Dropping a stored procedure	DROP PROCEDURE
Recompiling a stored procedure	ALTER PROCEDURE

Defining a Function

In GaussDB, a function is similar to a stored procedure, which is a set of SQL statements. The function and stored procedure are used the same. For details about related SQL statements, see Table 10.

**Table 10** SQL statements for defining a function
Function	SQL Statement
Creating a function	CREATE FUNCTION
Altering a function attribute	ALTER FUNCTION
Dropping a function	DROP FUNCTION

Defining a Package

A package consists of the package specification and package body. It is used to manage stored procedures and functions by class, which is similar to classes in languages such as Java and C++.

**Table 11** SQL statements for defining a package
Function	SQL Statement
Creating a package	CREATE PACKAGE
Deleting a package	DROP PACKAGE
Altering a package attribute	ALTER PACKAGE

Defining a View

A view is a virtual table exported from one or more basic tables. It is used to control data accesses of users. Table 12 lists the related SQL statements.

**Table 12** SQL statements for defining a view
Function	SQL Statement
Creating a view	CREATE VIEW
Dropping a view	DROP VIEW

Defining a Cursor

To process SQL statements, the stored procedure process assigns a memory segment to store context association. Cursors are handles or pointers to context regions. With a cursor, the stored procedure can control alterations in context areas. For details, see Table 13.

**Table 13** SQL statements for defining a cursor
Function	SQL Statement
Creating a cursor	CURSOR
Moving a cursor	MOVE
Fetching data from a cursor	FETCH
Closing a cursor	CLOSE

Defining an Aggregate Function

**Table 14** SQL statements for defining an aggregate function
Function	SQL Statement
Creating an aggregate function	CREATE AGGREGATE
Modifying an aggregate function	ALTER AGGREGATE
Deleting an aggregate function	DROP AGGREGATE

Defining Data Type Conversion

**Table 15** SQL statements for defining a data type
Function	SQL Statement
Creating user-defined data type conversion	CREATE CAST
Deleting user-defined data type conversion	DROP CAST

Defining a Plug-in Extension

The extended function is for internal use only. You are advised not to use it.

**Table 16** SQL statements for defining a plug-in extension
Function	SQL Statement
Creating a plug-in extension	CREATE EXTENSION
Modifying a plug-in extension	ALTER EXTENSION
Deleting a plug-in extension	DROP EXTENSION

Defining an Operator

**Table 17** SQL statements for defining an operator
Function	SQL Statement
Creating an operator	CREATE OPERATOR
Modifying an operator	ALTER OPERATOR
Deleting an operator	DROP OPERATOR

Defining a Data Type

**Table 18** SQL statements for defining a data type
Function	SQL Statement
Creating a data type	CREATE TYPE
Modifying a data type	ALTER TYPE
Deleting a data type	DROP TYPE

Defining a Scheduled Task

**Table 19** SQL statements for defining a scheduled task
Function	SQL Statement
Creating a scheduled task	CREATE EVENT
Modifying a scheduled task	ALTER EVENT
Deleting a scheduled task	DROP EVENT

Defining a Database Link

A database link can be used to remotely operate a database object. For details about corresponding SQL statements, see Table 20.

**Table 20** Database link-related SQL statements
Function	SQL Statement
Creating a database link	CREATE DATABASE LINK
Modifying a database link	ALTER DATABASE LINK
Deleting a database link	DROP DATABASE LINK

Defining a Foreign Data Wrapper

**Table 21** SQL statements related to the foreign data wrapper
Function	SQL Statement
Creating a foreign data wrapper	CREATE FOREIGN DATA WRAPPER
Modifying a foreign data wrapper	ALTER FOREIGN DATA WRAPPER
Deleting a foreign data wrapper	DROP FOREIGN DATA WRAPPER