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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, index, or view.

GaussDB(DWS) does not support DDL if its CN is unavailable. For example, if a CN in the cluster is faulty, creating a database or table will fail.

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. The following table lists the related SQL statements.

Table 1 SQL statements for defining a database

Function

SQL Statement

Create a database

CREATE DATABASE

Alter database attributes

ALTER DATABASE

Delete 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. The following table lists the related SQL statements.

Table 2 SQL statements for defining a schema

Function

SQL Statement

Create a schema

CREATE SCHEMA

Alter schema attributes

ALTER SCHEMA

Delete a schema

DROP SCHEMA

Defining a Table

A table is a special data structure in a database and is used to store data objects and the relationship between data objects. The following table lists the related SQL statements.

Table 3 SQL statements for defining a table

Function

SQL Statement

Create a table

CREATE TABLE

Alter table attributes

ALTER TABLE

Alter a table name

RENAME TABLE

Delete a table

DROP TABLE

Delete all the data from a table

TRUNCATE

Defining a Partitioned Table

A partitioned table is a special data structure in a database and is used to store data objects and the relationship between data objects. The following table lists the related SQL statements.

Table 4 SQL statements for defining a partitioned table

Function

SQL Statement

Create a partitioned table

CREATE TABLE PARTITION

Editing a partition

ALTER TABLE PARTITION

Alter partitioned table attributes

ALTER TABLE PARTITION

Delete a partition

ALTER TABLE PARTITION

Delete a partitioned table

DROP TABLE

Defining an Index

An index indicates the sequence of values in one or more columns in the database table. The database index is a data structure that improves the speed of data access to specific information in a database table. The following table lists the related SQL statements.

Table 5 SQL statements for defining an index

Function

SQL Statement

Create an index

CREATE INDEX

Alter index attributes

ALTER INDEX

Delete an index

DROP INDEX

Rebuild an index

REINDEX

Defining a Role

A role is used to manage rights. For database security, all management and operation rights can be assigned to different roles. The following table lists the related SQL statements.

Table 6 SQL statements for defining a role

Function

SQL Statement

Create a role

CREATE ROLE

Alter role attributes

ALTER ROLE

Delete a role

DROP ROLE

Defining a User

A user is used to log in to a database. Different rights can be assigned to users for managing data accesses and operations of users. The following table lists the related SQL statements.

Table 7 SQL statements for defining a user

Function

SQL Statement

Create a user

CREATE USER

Alter user attributes

ALTER USER

Delete a user

DROP USER

Defining a Redaction Policy

Data redaction is to protect sensitive data by masking or changing data. You can create a data redaction policy for a specific table object and specify the effective scope of the policy. You can also add, modify, and delete redaction columns. The following table lists the related SQL statements.

Table 8 SQL statements for managing redaction policies

Function

SQL Statement

Create a data redaction policy

CREATE REDACTION POLICY

Modify a data redaction policy applied to a specified table

ALTER REDACTION POLICY

Delete a data redaction policy applied to a specified table

DROP REDACTION POLICY

Defining Row-Level Access Control

Row-level access control policies control the visibility of rows in database tables. In this way, the same SQL query may return different results for different users. The following table lists the related SQL statements.

Table 9 SQL statements for row-level access control

Function

SQL Statement

Create a row-level access control policy

CREATE ROW LEVEL SECURITY POLICY

Modify an existing row-level access control policy

ALTER ROW LEVEL SECURITY POLICY

Delete a row-level access control policy from a table

DROP ROW LEVEL SECURITY POLICY

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. The following table lists the related SQL statements.

Table 10 SQL statements for defining a stored procedure

Function

SQL Statement

Create a stored procedure

CREATE PROCEDURE

Delete a stored procedure

DROP PROCEDURE

Defining a Function

In GaussDB(DWS), a function is similar to a stored procedure, which is a set of SQL statements. The function and stored procedure are used the same. The following table lists the related SQL statements.

Table 11 SQL statements for defining a function

Function

SQL Statement

Create a function

CREATE FUNCTION

Alter function attributes

ALTER FUNCTION

Delete a function

DROP FUNCTION

Defining a View

A view is a virtual table exported from one or several basic tables. The view is used to control data accesses for users. The following table lists the related SQL statements.

Table 12 SQL statements for defining a view

Function

SQL Statement

Create a view

CREATE VIEW

Delete 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.

Table 13 SQL statements for defining a cursor

Function

SQL Statement

Create a cursor

CURSOR

Move a cursor

MOVE

Extract data from a cursor

FETCH

Close a cursor

CLOSE

Altering or Ending a Session

A session is a connection established between the user and the database. The following table lists the related SQL statements.

Table 14 SQL statements related to sessions

Function

SQL Statement

Alter a session

ALTER SESSION

End a session

ALTER SYSTEM KILL SESSION

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 following table lists the related SQL statements.

Table 15 SQL statements for defining a resource pool

Function

SQL Statement

Create a resource pool

CREATE RESOURCE POOL

Change resource attributes

ALTER RESOURCE POOL

Delete a resource pool

DROP RESOURCE POOL

Defining Synonyms

A synonym is a special database object compatible with Oracle. It is used to store the mapping between a database object and another. Currently, only synonyms can be used to associate the following database objects: tables, views, functions, and stored procedures. The following table lists the related SQL statements.

Table 16 SQL statements for managing synonyms

Function

SQL Statement

Creating a synonym

CREATE SYNONYM

Modifying a synonym

ALTER SYNONYM

Deleting a synonym

DROP SYNONYM

Defining Text Search Configuration

A text search configuration specifies a text search parser that can divide a string into tokens, plus dictionaries that can be used to determine which tokens are of interest for searching. The following table lists the related SQL statements.

Table 17 SQL statements for configuring text search

Function

SQL Statement

Create a text search configuration

CREATE TEXT SEARCH CONFIGURATION

Modify a text search configuration

ALTER TEXT SEARCH CONFIGURATION

Delete a text search configuration

DROP TEXT SEARCH CONFIGURATION

Defining a Full-text Retrieval Dictionary

A dictionary is used to identify and process specific words during full-text retrieval. Dictionaries are created by using predefined templates (defined in the PG_TS_TEMPLATE system catalog). Five types of dictionaries can be created, Simple, Ispell, Synonym, Thesaurus, and Snowball. Each type of dictionaries is used to handle different tasks. The following table lists the related SQL statements.

Table 18 SQL statements for a full-text search dictionary

Function

SQL Statement

Create a full-text retrieval dictionary

CREATE TEXT SEARCH DICTIONARY

Modify a full-text retrieval dictionary

ALTER TEXT SEARCH DICTIONARY

Delete a full-text retrieval dictionary

DROP TEXT SEARCH DICTIONARY
Parent topic: DDL Syntax