Insert, Update & Delete Records

1. What is DML?

DML (Data Manipulation Language) is used to retrieve, store, modify, and delete data in database tables.

• Works on table data
• Does not change table structure
• Common DML commands: INSERT, UPDATE, DELETE

2. INSERT INTO

The INSERT INTO command is used to add new records (rows) into a table.

2.1 Insert All Columns

INSERT INTO student
VALUES (101, 'Amit', 78);

2.2 Insert Specific Columns

INSERT INTO student (RollNo, Name)
VALUES (102, 'Riya');

• Order of values must match column order
• NULL allowed if column permits

3. Insert Multiple Records

INSERT INTO student (RollNo, Name, Marks)
VALUES
(103, 'Suman', 72),
(104, 'Neha', 85),
(105, 'Rahul', 90);

4. UPDATE

The UPDATE command modifies existing records in a table.

4.1 Update All Rows

UPDATE student
SET Marks = 80;

4.2 Update Specific Rows (Using WHERE)

UPDATE student
SET Marks = 88
WHERE RollNo = 102;

• WHERE clause is important
• Without WHERE, all rows are updated

5. DELETE

The DELETE command removes records from a table.

5.1 Delete All Records

DELETE FROM student;

5.2 Delete Specific Records

DELETE FROM student
WHERE RollNo = 105;

• Deletes rows, not table structure
• Can be rolled back (if transaction supported)

6. DELETE vs TRUNCATE

DELETE                         TRUNCATE
----------------------------  ---------------------------
DML command                   DDL command
Deletes selected rows         Deletes all rows
WHERE clause allowed          WHERE not allowed
Can be rolled back            Cannot be rolled back

7. Important Safety Tips

• Always use WHERE with UPDATE and DELETE
• Check records using SELECT before DELETE
• Take backup before mass update/delete

Practice Questions

1. What is DML?
2. Write syntax for INSERT command.
3. Why WHERE clause is important in UPDATE?
4. Differentiate DELETE and TRUNCATE.
5. How to insert multiple records?

Practice Task