SQL
Database Schema
- SQL defines the structure of a database using CREATE statements for tables, specifying columns and their data types.
- Relationships between tables are established using keys: primary keys uniquely identify records, while foreign keys establish relationships between tables.
Data Manipulation
| Command | Description |
|---|---|
| SELECT | Retrieves data from one or more tables based on specified criteria. |
| INSERT | Adds new records into a table. |
| UPDATE | Modifies existing records in a table. |
| DELETE | Removes records from a table. |
Data Definition
| Command | Description |
|---|---|
| CREATE | Defines new databases, tables, views, or indexes. |
| ALTER | Modifies existing database objects, such as tables. |
| DROP | Deletes databases, tables, views, or indexes. |
Data Control
| Command | Description |
|---|---|
| GRANT | Gives users access privileges to database objects. |
| REVOKE | Removes previously granted permissions. |
General Tips!
- Use Proper Indexing: Index frequently queried columns to improve query performance, but avoid over-indexing as it can slow down write operations.
- Write Efficient Queries: Optimize your queries by selecting only the necessary columns, avoiding SELECT *, and using joins wisely.
- Normalize Your Data: Organize your database into normalized tables to reduce redundancy and improve data integrity.
- Use Transactions: Ensure data consistency and integrity by wrapping multiple related operations in transactions, especially in multi-step processes.
- Understand and Use SQL Functions: Leverage built-in SQL functions for data manipulation and retrieval, such as aggregate functions (SUM, COUNT) and string functions (CONCAT, SUBSTRING).