Jassif Team Institution

let mysql = require('mysql');

let con = mysql.createConnection({
  host: "localhost",
  user: "yourusername",
  password: "yourpassword",
  database: "mydb"
});

con.connect(function(err) {
  if (err) throw err;
  let sql = "DELETE FROM customers WHERE address = 'Mountain 21'";
  con.query(sql, function (err, result) {
    if (err) throw err;
    console.log("Number of records deleted: " + result.affectedRows);
  });
});

C:\Users\Your Name>node demo_db_delete.js

Number of records deleted: 1

{
  fieldCount: 0,
  affectedRows: 1,
  insertId: 0,
  serverStatus: 34,
  warningCount: 0,
  message: '',
  protocol41: true,
  changedRows: 0
}

console.log(result.affectedRows)

1

// Delete by ID
let id = 5;
let sql = "DELETE FROM customers WHERE id = ?";
con.query(sql, [id], function (err, result) {
  if (err) throw err;
  console.log("Records deleted: " + result.affectedRows);
});

// Delete multiple records with IN operator
let ids = [1, 3, 7];
let sql = "DELETE FROM customers WHERE id IN (?)";
con.query(sql, [ids], function (err, result) {
  if (err) throw err;
  console.log("Records deleted: " + result.affectedRows);
});

// Delete with range condition
let sql = "DELETE FROM customers WHERE id BETWEEN 10 AND 20";
con.query(sql, function (err, result) {
  if (err) throw err;
  console.log("Records deleted: " + result.affectedRows);
});

// Delete with multiple conditions
let name = 'John';
let minDate = '2023-01-01';
let sql = "DELETE FROM orders WHERE customer_name = ? AND order_date < ?";
con.query(sql, [name, minDate], function (err, result) {
  if (err) throw err;
  console.log("Records deleted: " + result.affectedRows);
});

// Delete using LIKE operator
let pattern = '%test%';
let sql = "DELETE FROM products WHERE description LIKE ?";
con.query(sql, [pattern], function (err, result) {
  if (err) throw err;
  console.log("Records deleted: " + result.affectedRows);
});

// First check what will be deleted
let id = 5;
con.query("SELECT * FROM customers WHERE id = ?", [id], function (err, result) {
  if (err) throw err;
  
  if (result.length > 0) {
    console.log("Will delete:", result[0]);
    
    // Then proceed with deletion
    con.query("DELETE FROM customers WHERE id = ?", [id], function (err, deleteResult) {
      if (err) throw err;
      console.log("Records deleted: " + deleteResult.affectedRows);
    });
  } else {
    console.log("No records found to delete");
  }
});

// Using transactions for safe deletion
con.beginTransaction(function(err) {
  if (err) throw err;
  
  let sql = "DELETE FROM customers WHERE id = ?";
  con.query(sql, [5], function (err, result) {
    if (err) {
      return con.rollback(function() {
        throw err;
      });
    }
    
    console.log("Records deleted: " + result.affectedRows);
    
    // Commit the transaction
    con.commit(function(err) {
      if (err) {
        return con.rollback(function() {
          throw err;
        });
      }
      console.log("Transaction completed successfully");
    });
  });
});

// Soft delete (update a flag instead of actual deletion)
let id = 5;
let sql = "UPDATE customers SET deleted = 1 WHERE id = ?";
con.query(sql, [id], function (err, result) {
  if (err) throw err;
  console.log("Records soft deleted: " + result.affectedRows);
});

// Then query only non-deleted records
con.query("SELECT * FROM customers WHERE deleted = 0", function (err, result) {
  if (err) throw err;
  console.log("Active customers:", result);
});

const mysql = require('mysql');

// Create connection
const con = mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "password",
  database: "company_db"
});

// Connect to MySQL
con.connect((err) => {
  if (err) {
    console.error('Error connecting to MySQL:', err.message);
    return;
  }
  
  console.log('Connected to MySQL database');
  
  // Example 1: Basic DELETE with WHERE
  console.log('\n1. Deleting customer with specific address:');
  const address = 'Mountain 21';
  con.query("DELETE FROM customers WHERE address = ?", [address], (err, result) => {
    if (err) {
      console.error('Error in delete 1:', err.message);
      return;
    }
    console.log(`Records deleted: ${result.affectedRows}`);
    console.log('Result object:', result);
  });
  
  // Example 2: DELETE with transaction
  console.log('\n2. Safe deletion with transaction:');
  con.beginTransaction((err) => {
    if (err) {
      console.error('Error starting transaction:', err.message);
      return;
    }
    
    // First check what we're deleting
    const customerId = 5;
    con.query("SELECT * FROM customers WHERE id = ?", [customerId], (err, selectResult) => {
      if (err) {
        return con.rollback(() => {
          console.error('Error in select:', err.message);
        });
      }
      
      if (selectResult.length > 0) {
        console.log('Will delete customer:', selectResult[0]);
        
        // Perform deletion
        con.query("DELETE FROM customers WHERE id = ?", [customerId], (err, deleteResult) => {
          if (err) {
            return con.rollback(() => {
              console.error('Error in delete:', err.message);
            });
          }
          
          console.log(`Transaction - Records deleted: ${deleteResult.affectedRows}`);
          
          // Commit transaction
          con.commit((err) => {
            if (err) {
              return con.rollback(() => {
                console.error('Error committing transaction:', err.message);
              });
            }
            console.log('Transaction committed successfully');
            
            // Close connection
            setTimeout(() => {
              con.end((err) => {
                if (err) {
                  console.error('Error closing connection:', err.message);
                  return;
                }
                console.log('\nConnection closed');
              });
            }, 1000);
          });
        });
      } else {
        console.log('No customer found with ID:', customerId);
        con.rollback(() => {
          console.log('Transaction rolled back');
        });
      }
    });
  });
});