In SQL (Structured Query Language), there is no part directly called "sub-language" specifically for managing database access. However, SQL itself is a language for managing databases, and it contains multiple parts or functions, which can be regarded as supporting different aspects of database access in a broad sense.
Specifically, SQL provides the following major functional modules, which can be regarded as sub-functions or sub-languages for managing database access (although they are not usually called this directly):
1. Data Definition Language (DDL): DDL is used to define or modify the structure of the database, including creating, modifying, and deleting table structures, indexes, etc. This is the first step in managing database access because it establishes the structure of the database so that data can be stored and accessed according to certain rules. For example, statements such as `CREATE TABLE`, `ALTER TABLE`, and `DROP TABLE` all belong to DDL.
2. Data Manipulation Language (DML): DML is used to insert, update, and delete data in the database. These operations directly affect the data in the database and are the main way for users or applications to interact with the database. For example, statements such as `INSERT INTO`, `UPDATE`, and `DELETE` all belong to DML.
3. Data Query Language (DQL): Although DQL is not usually considered an independent sub-language of SQL, it is a key part of SQL for querying data. DQL provides the ability to retrieve data from the database through the `SELECT` statement and is one of the most commonly used functions in database access.
4. Data Control Language (DCL): DCL is used to define the access rights and security levels of the database, including granting and revoking user permissions. Although it does not directly participate in the storage and retrieval of data, it is an important means of managing database access security. For example, statements such as `GRANT` and `REVOKE` all belong to DCL.
5. Transaction Control Language (TCL): TCL is used to manage database transactions, including starting transactions, committing transactions, and rolling back transactions. Transactions are an important concept in database operations, which ensure the consistency and integrity of data. For example, statements such as `BEGIN TRANSACTION`, `COMMIT`, `ROLLBACK` (in database systems that support these statements) belong to TCL.
In summary, although SQL does not have a part directly called "sub-language" specifically for managing database access, its various functional modules (such as DDL, DML, DQL, DCL and TCL) together constitute a complete system for managing database access. These functional modules work together to make SQL a powerful and flexible database management language.