SQL
Example - Select Queries
1. Select all columns from a table:
SELECT * FROM employees;
2. Select specific columns:
SELECT first_name, last_name FROM employees;
3. Select with a condition:
SELECT first_name, last_name FROM employees WHERE age > 30;
4. Select with sorting:
SELECT first_name, last_name FROM employees ORDER BY last_name ASC;
5. Select with grouping:
SELECT department, COUNT(*) FROM employees GROUP BY department;
6. Select with grouping and filtering:
SELECT department, COUNT(*) FROM employees GROUP BY department HAVING COUNT(*) > 5;
7. Select with limit:
SELECT first_name, last_name FROM employees LIMIT 10;
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).