SQL
Database Table
Database tables are the primary storage objects within a relational database, where data is organized into a structured format consisting of rows and columns. Each table represents a specific type of data and can be related to other tables through foreign keys. Here’s a more detailed explanation of database tables:
Structure of a Database Table
-
Columns (Fields/Attributes):
- Definition: Columns define the data type and constraints for a specific piece of data stored in the table.
- Attributes: Each column has a name, data type (e.g., INTEGER, VARCHAR, DATE), and optional constraints (e.g., PRIMARY KEY, NOT NULL).
-
Rows (Records/Tuples):
- Definition: Rows represent individual entries or records in the table.
- Attributes: Each row contains data for each column defined in the table.
Example of a Database Table
| EmployeeID | FirstName | LastName | DepartmentID | Salary | HireDate |
|---|---|---|---|---|---|
| 1 | John | Doe | 1 | 60000.00 | 2021-01-11 |
| 2 | Jane | Smith | 2 | 65000.00 | 2019-03-21 |
| 3 | Emily | Smith | 3 | 62000.00 | 2020-11-27 |
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).