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 a CN in the cluster is faulty, creating a database or a table will fail.

Defining a client master key (CMK).

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 Column Encryption Key (CEK)

CEKs are used to encrypt data for the encrypted database feature. CEK definition includes creating and deleting 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
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 common 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

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 function attributes	ALTER FUNCTION
Dropping a function	DROP FUNCTION

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 11 lists the related SQL statements.

**Table 11** 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 12.

**Table 12** 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 a Resource Pool

A resource pool is a system catalog used by the resource load management module to specify attributes related to resource management, such as Cgroups. (The current feature is a lab feature. Contact Huawei technical support before using it.) For details about related SQL statements, see Table 13.

**Table 13** SQL statements for defining a resource pool
Function	SQL Statement
Creating a resource pool	CREATE RESOURCE POOL
Altering resource attributes	ALTER RESOURCE POOL
Dropping a resource pool	DROP RESOURCE POOL

Defining a Workload Group

A workload group is a system catalog used by the resource load management module to specify the number of concurrent SQL statements in the associated resource pool. (The current feature is a lab feature. Contact Huawei technical support before using it.) For details about related SQL statements, see Table 14.

**Table 14** SQL statements for defining a workload group
Function	SQL Statement
Creating a workload group	CREATE WORKLOAD GROUP
Altering the attributes of a workload group	ALTER WORKLOAD GROUP
Dropping a workload group	DROP WORKLOAD GROUP

Defining Application Mapping

Application mapping is a system catalog used by the resource load management module to associate with a workload group. (The current feature is a lab feature. Contact Huawei technical support before using it.) After a user connects to a database, the user can specify a workload group to associate SQL statements to certain resources. For details about related SQL statements, see Table 15.

**Table 15** SQL statements for defining application mapping
Function	SQL Statement
Creating application mapping	CREATE APP WORKLOAD GROUP MAPPING
Altering application mapping attributes	ALTER APP WORKLOAD GROUP MAPPING
Dropping application mapping	DROP APP WORKLOAD GROUP MAPPING