SQL (Structured Query Language) is the standard language for managing and manipulating databases. SQL commands can be categorized into different types based on their functionality. Understanding these commands is crucial for database administrators and developers to perform database operations efficiently.
1. Data Definition Language (DDL)
DDL commands are used to define and modify the database structure. These commands deal with schema-related operations.
| Command | Description |
|---|---|
CREATE | Creates a new database object like a table, view, or index. |
ALTER | Modifies an existing database object such as adding or removing columns. |
DROP | Deletes an entire database object like a table. |
TRUNCATE | Removes all records from a table without logging individual row deletions. |
COMMENT | Adds comments to the database schema. |
RENAME | Renames a database object. |
2. Data Manipulation Language (DML)
DML commands deal with data modification and manipulation within tables.
| Command | Description |
INSERT | Adds new records into a table. |
UPDATE | Modifies existing records. |
DELETE | Removes records from a table. |
MERGE | Combines INSERT and UPDATE functionality into a single operation. |
3. Data Query Language (DQL)
DQL is used to retrieve data from the database.
| Command | Description |
SELECT | Retrieves data from one or more tables. |
4. Data Control Language (DCL)
DCL commands manage permissions and access control.
| Command | Description |
GRANT | Provides specific privileges to users. |
REVOKE | Removes previously granted privileges. |
5. Transaction Control Language (TCL)
TCL commands manage transactions in SQL.
| Command | Description |
COMMIT | Saves all changes made during the transaction. |
ROLLBACK | Undoes changes in a transaction if an error occurs. |
SAVEPOINT | Creates a temporary save point within a transaction. |
SET TRANSACTION | Defines transaction properties. |
Final Thoughts
Understanding SQL commands is essential for managing databases effectively. From defining tables to controlling user access, each type of SQL command plays a significant role in database management.
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For additional resources, check out this Comprehensive Guide on SQL Commands for further learning.