SQL Data Manipulation (INSERT, UPDATE, DELETE) Explained with Examples + Practice Questions

When to Use Data Manipulation

• Use INSERT to add new data
• Use UPDATE to modify existing data
• Use DELETE to remove data

These operations are used in:

• Backend systems
• Database management
• Real-world applications

Example Dataset

Table: employees

INSERT (Add Data)

Insert a New Row

sql
INSERT INTO employees (id, name, department, salary)
VALUES (4, 'Emma', 'Finance', 70000);

Insert Multiple Rows

sql
INSERT INTO employees (id, name, department, salary)
VALUES
(5, 'David', 'HR', 45000),
(6, 'Ankit', 'IT', 52000);

Key Points:

• Must match column order
• Required columns cannot be NULL
• Always specify column names (best practice)

UPDATE (Modify Data)

Update Specific Row

sql
UPDATE employees
SET salary = 65000
WHERE name = 'Alice';

Update Multiple Columns

sql
UPDATE employees
SET department = 'Finance', salary = 70000
WHERE id = 3;

Key Points:

• Always use WHERE
• Without WHERE, all rows will be updated

DELETE (Remove Data)

Delete Specific Row

sql
DELETE FROM employees
WHERE id = 2;

Delete Multiple Rows

sql
DELETE FROM employees
WHERE department = 'HR';

Key Points:

• Always use WHERE
• Without WHERE, deletes all rows

INSERT vs UPDATE vs DELETE

Combining with Conditions

sql
UPDATE employees
SET salary = salary + 5000
WHERE department = 'IT';

Key Concepts

• INSERT adds data
• UPDATE modifies data
• DELETE removes data
• WHERE is critical to avoid mistakes

Practice Note

For safety, these exercises preview the effect using SELECT queries. When write actions are enabled later, you can swap them to real INSERT/UPDATE/DELETE.