Table Integrity Constraints Enforce data validity through constraint definitions: Unique Constraints Prevent duplicate values in specific columns: ALTER TABLE personnel ADD CONSTRAINT uk_email UNIQUE (email_address); Check Constraints Validate data against boolean expressions: ALTER TABLE personnel...
MyBatis-Plus provides a robust abstraction layer over standard MyBatis operations through its Wrapper API, enabling programmatic SQL generation without XML configuration. The architecture centers around the Wrapper abstract class, which serves as the foundasion for all condition constructors. Class...
Data Insertion (INSERT) Adding records to a database table utilizes the INSERT statement. It allows explicit column targeting or full-row insertion. Multiple rows can be added in a single transaction for improved efficiency. INSERT INTO staff_directory (employee_id, department_code, full_name, offic...
Data Schema ride_requests table: user_id: Passenger identifier location: City name request_ts: Timestamp of ride request request_end_ts: Timestamp when request period ends booking_id: Unique order identifier (null until accepted) ride_orders table: booking_id: Unique order identifier user_id: Passen...
The objective is to compute the completion rate for each video that had play activity in 2021, rounded to three decimal places, and order the results in descending order. The completion rate is defined as the proportion of plays where the viewing duration was greater than or equal to the video's len...
Data Query Language (DQL) DQL (Data Query Language) is used to retrieve records from database tables. The primary keyword for queries is SELECT. Query operations are fundamental in database systems, often used more frequently than insert, update, or delete operations. Data displayed on websites and...
ACID Principles of Database Transactions A transaction represents a cohesive unit of database operations that must execute entirely or not at all. This unit adheres to four fundamental principles, commonly abbreviated as ACID. Atomicity: All operations within the work unit are treated as a single in...
Data Retrieval Fundamentals Retrieve specific columns from a dataset: SELECT first_name, last_name, email FROM employees; Eliminate duplicate values from results: SELECT DISTINCT department_id FROM employees; Filter records based on conditions: SELECT product_name, unit_price FROM inventory WHERE un...
Pagination Based on Auto-Incrementing Primary Keys Applicability: Use when the primary key is auto-incrementing and sequential, and results are sorted by the primary key. Example query: SELECT * FROM users LIMIT 90000, 5; This query retrieves 5 records starting from the 90,001st row. The LIMIT claus...
Creating Depratment and Employee Tables with Data Insetrion 1. Departmant Table Creation CREATE TABLE departments ( department_id INT PRIMARY KEY AUTO_INCREMENT COMMENT 'Department ID', department_name VARCHAR(50) COMMENT 'Department Name' ); 2. Inserting Department Data INSERT INTO departments (dep...