Summary of 2. SQL DML Commands Insert, Update, Delete, and Intro to SELECT

Summary of "2. SQL DML Commands INSERT, UPDATE, DELETE, and Intro to SELECT"

This video provides a comprehensive introduction to SQL Data Manipulation Language (DML) commands—INSERT, UPDATE, DELETE, and an introduction to the SELECT command. It explains the purpose, syntax, and practical use of each command with examples, emphasizing the importance of conditions (WHERE clause) in UPDATE and DELETE operations to avoid unintended data modification or loss. The video also demonstrates creating a sample table and executing queries using MySQL.

Main Ideas and Concepts

• SQL Overview
  • SQL (Structured Query Language) is essential for managing and retrieving data in relational databases.
  • SQL has multiple components: DDL (Data Definition Language) for structure/schema and DML (Data Manipulation Language) for data operations.
• Difference Between DDL and DML
  • DDL commands manage the database structure (e.g., creating or deleting tables).
  • DML commands manipulate the data inside tables (INSERT, UPDATE, DELETE, SELECT).
• DML Commands Covered
  1. INSERT
     • Used to add new data rows into a table.
     • Syntax:
       INSERT INTO table_name (column1, column2, ...) VALUES (value1, value2, ...);
     • Notes on values:
       • Strings and dates require single quotes.
       • Date format: YYYY-MM-DD.
       • Numbers can be written directly without quotes.
  2. UPDATE
     • Modifies existing data in a table.
     • Syntax:
       UPDATE table_name SET column1 = value1, column2 = value2 WHERE condition;
     • Emphasizes the importance of the WHERE clause to UPDATE specific rows only.
  3. DELETE
     • Removes rows from a table.
     • Syntax:
       DELETE FROM table_name WHERE condition;
     • Warning: Without WHERE clause, all rows will be deleted.
  4. SELECT
     • Retrieves data from one or more tables.
     • Syntax:
       SELECT column1, column2, ... FROM table_name WHERE condition;
     • SELECT * returns all columns.
     • Allows selective retrieval by specifying columns and filtering rows with conditions.
     • Supports logical operators (AND, OR) and comparison operators.
• Selection and Projection Concepts
  • Selection: Filtering rows based on conditions (WHERE clause).
  • Projection: Choosing specific columns to display.
• Table Creation and Data Types
  • Example table employees with columns:
    • employee_id (integer)
    • employee_name (varchar)
    • date_of_joining (date)
    • salary (decimal)
    • bio (text)
  • Demonstrates data insertion into this table.
• Practical Examples
  • Inserting employees with various data types.
  • Updating salary for a specific employee.
  • Deleting an employee record safely using WHERE clause.
  • Selecting all rows or filtered rows using conditions.
  • Combining multiple conditions using AND/OR.
  • Illustrating the effect of missing WHERE clause in UPDATE and DELETE commands.
• Best Practices
  • Always use WHERE clause in UPDATE and DELETE commands to avoid unintended changes.
  • Use single quotes for string and date literals.
  • Understand date format and data types while inserting.
• Next Topics Preview
  • ORDER BY clause for sorting results.
  • Aggregate functions.
  • GROUP BY commands.

Detailed Methodology / Instructions for DML Commands

• INSERT Command
  • Syntax:
    

    INSERT INTO table_name (column1, column2, ..., columnN) 
    VALUES (value1, value2, ..., valueN);
            

  • Use single quotes for strings and dates.
  • Date format: YYYY-MM-DD.
  • Example:
    

    INSERT INTO employees (employee_id, employee_name, date_of_joining, salary, bio)
    VALUES (1, 'Sund', '2014-12-30', 55000.00, 'Sund is a highly skilled software engineer');
            

• UPDATE Command
  • Syntax:
    

    UPDATE table_name 
    SET column1 = value1, column2 = value2, ...
    WHERE condition;
            

  • Always include WHERE clause to target specific rows.
  • Example:
    

    UPDATE employees 
    SET salary = 60000 
    WHERE employee_id = 1;
            

• DELETE Command
  • Syntax:
    

    DELETE FROM table_name 
    WHERE condition;
            

  • Always include WHERE clause to avoid deleting all rows.
  • Example:
    

    DELETE FROM employees 
    WHERE employee_id = 1;
            

Category

Educational

Video