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UPDATE modifies existing rows in a table. DELETE removes rows. ALWAYS use WHERE with UPDATE and DELETE — without it, you will update or delete ALL rows in the table! This is one of the most common and dangerous mistakes in SQL.

UPDATE & DELETE Syntax

UPDATE table SET col=val WHERE condition — Modify rows

DELETE FROM table WHERE condition — Remove rows

⚠️ Always use WHERE! Without it, ALL rows are affected

UPDATE can change multiple columns: SET col1=val1, col2=val2

Use SELECT first to verify which rows will be affected

TRUNCATE TABLE — Deletes all rows (faster than DELETE without WHERE)

UPDATE & DELETE Examples

Example

-- Update Alice's grade to 'A+'
UPDATE students
SET grade = 'A+'
WHERE name = 'Alice';

-- Update multiple columns at once
UPDATE students
SET age = 23, city = 'Pune'
WHERE id = 2;

-- ⚠️ DANGEROUS: This updates ALL rows!
-- UPDATE students SET grade = 'F';  -- DON'T DO THIS!

-- Delete a specific student
DELETE FROM students
WHERE id = 3;

-- Delete all students from Delhi
DELETE FROM students
WHERE city = 'Delhi';

-- ⚠️ DANGEROUS: This deletes ALL rows!
-- DELETE FROM students;  -- DON'T DO THIS!

-- Verify changes
SELECT * FROM students;

Try It Yourself: UPDATE & DELETE

Try It Yourself: UPDATE & DELETEJavaScript

JavaScript Editor

✓ ValidTab = 2 spaces

// Simulating UPDATE and DELETE in JavaScript

let students = [
  { id: 1, name: "Alice",   age: 20, city: "Mumbai",    grade: "A" },
  { id: 2, name: "Bob",     age: 22, city: "Delhi",     grade: "B" },
  { id: 3, name: "Charlie", age: 19, city: "Bangalore", grade: "A" },
  { id: 4, name: "Diana",   age: 21, city: "Mumbai",    grade: "C" },
];

function showAll() {
    students.forEach(s => console.log(`${s.id}. ${s.name} | ${s.city} | Grade:${s.grade}`));
}

console.log("=== Before Changes ===");
showAll();

// UPDATE students SET grade='A+' WHERE name='Alice'
students = students.map(s =>
    s.name === "Alice" ? { ...s, grade: "A+" } : s
);

// DELETE FROM students WHERE city='Delhi'
students = students.filter(s => s.city !== "Delhi");

console.log("\n=== After UPDATE & DELETE ===");
showAll();
console.log("Remaining rows:", students.length);

Result

Click ▶ Run to see the result

Edit the code on the left, then click Run

JavaScript|27 lines|857 chars|✓ Valid syntax

UTF-8

UPDATE & DELETE

UPDATE and DELETE

UPDATE & DELETE Syntax

UPDATE & DELETE Examples

Try It Yourself: UPDATE & DELETE

Quick Quiz