SQL
Inserting Data from Another Table
You can also insert data into a table from another table using a SELECT statement:
INSERT INTO employees (first_name, last_name, age, department)
SELECT first_name, last_name, age, department
FROM new_employees;
Handling NULL Values
If you want to insert NULL values into specific columns, just use the NULL keyword:
INSERT INTO employees (first_name, last_name, age, department)
VALUES ('Tom', 'Harris', NULL, 'Engineering');
Inserting Default Values
If a column has a default value and you want to insert the default value, you can omit that column from the INSERT statement:
INSERT INTO employees (first_name, last_name, department)
VALUES ('Emily', 'Clark', 'Sales');
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).